Effects of ouabain and calcium on potassium balance of isolated guinea pig ventricle

Isolated guinea pig ventricles were perfused as follows: A—45 min with normal Krebs-Ringer solution containing tracer amounts of K42 (NKR*); B—15 min with NKR*, 15 min with KR* in which half the calcium was replaced with sodium (Ca/2-KR*), 15 min with NKR*; C—15 min with NKR*, 15 min with Ca/2-KR*, 15 min with Ca/2-KR* + 10–6 m ouabain; D—15 min with NKR*, 15 min with NKR* + 3.4 x 10–4 m pentobarbital (PB), 15 min with NKR* + PB + ouabain. K influx, net K loss, contraction height, and flow rate were determined, and K efflux was calculated. Decreasing the external calcium concentration ([Ca]e) decreased K efflux with no effect on K influx; restoring [Ca]e increased K efflux without affecting influx. Ouabain decreased K influx more than it decreased K efflux. If [Ca]e was constant, reducing the contraction height with PB did not affect K movements. These findings are consistent with the hypotheses that: 1) calcium and potassium can compete for fixed intracellular anionic binding sites and 2) calcium and ouabain produce their effects on K movements by different means.

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Effects of Ca2+ and catecholamines on the guinea pig atrium action potential plateau

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1977.233.2.h203 ◽

1977 ◽

Vol 233 (2) ◽

pp. H203-H210

Author(s):

R. B. Robinson ◽

W. W. Sleator

Keyword(s):

Guinea Pig ◽

Calcium Concentration ◽

Potassium Conductance ◽

Slow Inward Current ◽

Activation Process ◽

Action Potential Plateau ◽

Guinea Pig Atrium ◽

Opposing Effects ◽

Guinea Pig Atria ◽

External Calcium

The activation process in isolated electrically driven guinea pig atria was studied by means of simultaneous microelectrode and tension recording. Reducing external calcium from 2.5 to 1.25 mM prolonged the plateau but further reduction of calcium shortened it. Progressively increasing doses of the calcium antagonist D600 (up to 1.4 micrometer), however, monotonically decreased plateau duration. Either protocol monotonically decreased steady-state tension, but with markedly different effects on the restitution relation. Epinephrine, and to a lesser extent isoproterenol, restored plateau duration after exposure to either a calcium-free or D600-containing solution, but only the isoproterenol effect was propranolol sensitive. Addition of calcium chelators enhanced rather than prevented the effect of epinephrine on plateau duration in a calcium-free solution, extending the plateau duration to more than 3 times normal in some cases. These results are explained in terms of two opposing effects of a change in calcium concentration on plateau formation, one action being through the slow inward current and the second through a shift in a calcium dependence of the inward-rectifying, potassium conductance system.

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Negative inotropic effect of extracellular calcium buffering in cardiac muscle

AJP Cell Physiology ◽

10.1152/ajpcell.1987.252.2.c248 ◽

1987 ◽

Vol 252 (2) ◽

pp. C248-C252 ◽

Cited By ~ 10

Author(s):

Y. Shimoni ◽

S. Ginsburg

Keyword(s):

Guinea Pig ◽

Cardiac Muscle ◽

Heart Muscle ◽

Calcium Concentration ◽

Negative Inotropic Effect ◽

Intracellular Acidosis ◽

Calcium Buffering ◽

The Mean ◽

Frog Atrium ◽

External Calcium

Heart muscle contracts more vigorously when calcium levels are raised. A transient depletion of calcium from restricted extracellular spaces occurs with each contraction. We decided to maintain the concentration of this ion at a constant level by using an external calcium buffering system. It was found that buffering calcium at a millimolar level (using citrate as a buffer) caused a decrease, rather than an increase in the strength of contraction. The mean reduction in peak tension was by 27% in guinea pig and by 50.5% in frog atrium. This finding is analyzed; its most plausible explanation is the hypothesis that the buffer dissipates a calcium inhomogeneity, consisting of a higher calcium concentration adjacent to the membrane. Alternative interpretations such as intracellular acidosis, were tested experimentally and ruled out.

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THE EFFECT OF HARMINE ON THE ACTION POTENTIAL OF THE GUINEA-PIG ATRIAL MUSCLE DEPENDS ON THE EXTERNAL CALCIUM CONCENTRATION

British Journal of Pharmacology ◽

10.1111/j.1476-5381.1981.tb09986.x ◽

1981 ◽

Vol 74 (2) ◽

pp. 415-418 ◽

Cited By ~ 1

Author(s):

ROBERT G. CARPENTIER

Keyword(s):

Guinea Pig ◽

Action Potential ◽

Calcium Concentration ◽

Atrial Muscle ◽

External Calcium

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Calcium uptake by mitochondria isolated from muskrat and guinea pig hearts

Journal of Experimental Biology ◽

10.1242/jeb.157.1.133 ◽

1991 ◽

Vol 157 (1) ◽

pp. 133-142

Author(s):

T. A. McKean

Keyword(s):

Guinea Pig ◽

Calcium Concentration ◽

Calcium Uptake ◽

Membrane Damage ◽

Indirect Measurements ◽

45Ca Uptake ◽

Hypoxia Ischemia ◽

Interfibrillar Mitochondria ◽

External Calcium

Subsarcolemmal and interfibrillar mitochondria were isolated from the hearts of the diving muskrat and non-diving guinea pig and direct and indirect measurements of calcium uptake were examined in vitro. The calcium-stimulated respiration rate and 45Ca uptake were measured and found to be greater in muskrat than in guinea pig mitochondria. Muskrat mitochondria were able to endure a greater external calcium concentration than guinea pig mitochondria before exhibiting indications of inner membrane damage. Calcium uptake by muskrat heart mitochondria was inhibited more by 1 mmoll-1 MgCl2 than was uptake by guinea pig mitochondria. No differences were detected between the interfibrillar and subsarcolemmal populations of mitochondria within species. An increased ability to sequester calcium by mitochondria without causing them damage may aid an animal during recovery from hypoxia, ischemia or acidosis.

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ABOLITION OF MAGNESIUM-INDUCED HYPOCALCAEMIA BY ACUTE THYRO-PARATHYROIDECTOMY IN THE CAT

Acta Endocrinologica ◽

10.1530/acta.0.0640150 ◽

1970 ◽

Vol 64 (1) ◽

pp. 150-158 ◽

Cited By ~ 3

Author(s):

S. Pors Nielsen

Keyword(s):

Sodium Chloride ◽

Flow Rate ◽

Magnesium Chloride ◽

Calcium Concentration ◽

Plasma Calcium ◽

Magnesium Concentration ◽

Isotonic Sodium Chloride ◽

Plasma Calcium Concentration ◽

High Concentrations ◽

Plasma Magnesium

ABSTRACT Intravenous infusion of isotonic magnesium chloride into young cats with a resultant mean plasma magnesium concentration of 7.7 meq./100 g protein was followed by a significant lowering of the plasma calcium concentration in 90 minutes. The rate of decrease of plasma calcium is consistent with the hypothesis that calcitonin is released by magnesium in high concentrations. There was no decrease in the plasma calcium concentration in cats of the same weight thyroparathyroidectomized 60 min before an identical magnesium chloride infusion or an infusion of isotonic sodium chloride at the same flow rate. The hypercalciuric effect of magnesium could not account for the hypocalcaemic effect of magnesium. Plasma magnesium concentration during magnesium infusion into cats with an intact thyroid-parathyroid gland complex was slightly, but not significantly higher than in acutely thyroparathyroidectomized cats.

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