Cat Heart Muscle in Vitro

Abstract

The cells of cat right ventricular papillary muscles were depleted of K and caused to accumulate Na and water by preincubation at 2-3°C. The time courses of changes in cellular ion content and volume and of the resting membrane potential (V,,) were then followed after abrupt rewarming to 27-28C. At physiological external K concentration ([K] = 5.32 mM) recovery of cellular ion and water contents was complete within 30 minutes, the maximal observable rates of K uptake and Na extrusion (Ammol cell ion/ (kg dry weight) (min.)) being 3.4 and 3.6, respectively. The recovery rate was markedly slowed at [K] = 1.0 mM. Rewarming caused Vm measured in cells at the muscle surface to recover within from < I1 to 9 minutes, but only slight restoration of cellular ion contents (measured in whole muscles) had occurred after 10 minutes. Studies of recovery in NaCl-free sucrose Ringer's solution made it possible to separate the ouabain-insensitive outward diffusion of Na as a salt from a simultaneous ouabain-sensitive Na extrusion which is associated with a net cellular K uptake. A hypothesis consistent with these observations is that rewarming may activate a ouabain-sensitive "electrogenic" mechanism, most probably the net active transport of Na out of the cell, from which net K uptake may then follow passively.The mechanism by which net movements of K ions are coupled to the extrusion of Na ions from the cell against an electrochemical gradient remains to be clarified in mammalian heart muscle. In the present study we have investigated this problem in cat right ventricular papillary muscle, using a modification of the method applied to frog skeletal muscle by Steinbach (1). Muscle cells were depleted of K and enriched in Na, C1, and water by preincubation at 2-3°C, then rapidly rewarmed to 27-28°C. The time courses of the net movements of ions and water during recovery from the effects of cooling, as well as of the transmembrane resting potential difference (Vm),

Na, K-ATPase activity, ATP and Pi concentrations in various regions of monkey heart and their relation to post-overdrive hyperpolarization.

“…In cardiac muscles, the active Na extrusion seemed to occur after a period of "Na loading" produced by several maneuvers (e.g., K-free perfusion, application of cardiac glycosides, lowering the temperature, and high frequency of stimulation) (PAGE and STORM, 1965;TAMAI and KAGIYAMA, 1968;GLITSCH, 1969GLITSCH, , 1972VASSALLE, 1970;CARPENTIER and VASSALLE, 1971;HIRAOKA and HECHT, 1973;AKASU et al, 1978;GADSBY and CRANEFIELD, 1979a, b;GLiTSCH and PUSCH,1980;NOSEK,1980). We assessed the Na, K-pump activities in both Epi and Endo from the hyperpolarization which followed high frequency drive ("post-overdrive hyperpo- during and after 1-min stimulation (3.3-3.8 Hz).. E1, E2, E3, and E4 show, respectively, the pre-stimulation diastolic membrane potential, the maximum depolarized potential during the stimulation, the potential at the end of the stimulation, and the maximum hyperpolarized potential after cessation of the stimulation.…”

“…There is a number of evidences showing that the active Na+ and K+ transport in cardiac muscles is electrogenic in that the extrusion of Na+ is not balanced by an equal uptake of K+ (PAGE and STORM, 1965;TAMAI and KAGIYAMA, 1968;VASSALLE, 1970;GLITSCH, 1972;HIRAOKA and HECHT, 1973). VASSALLE (1970) first described a post-overdrive hyperpolarization in sheep and dog Purkinje fibers and concluded that the activation of an electrogenic Na, K-pump was the major mechanism responsible for the post-overdrive hyperpolarization.…”

Activation of the electrogenic sodium pump in guinea‐pig atria by external potassium ions

“…This hyperpolarization occurs only if the intracellular Na concentration has been increased during cooling (Glitsch, 1972a). It is not due to the distribution of chloride ions at the sarcolemma (Page & Storm, 1965). The amplitude of hyperpolarization is correlated with the magnitude of active Na efflux from the rewarmed cardiac cells (Glitsch, 1972a).…”

“…The cell membrane of cardiac fibres hyperpolarizes transiently during rewarming after prolonged hypothermia (Page & Storm, 1965; Glitsch, 1969;Hiraoka & Hecht, H. G. GLITSCH AND OTHERS 1973). This hyperpolarization occurs only if the intracellular Na concentration has been increased during cooling (Glitsch, 1972a).…”

Characterization of the electrogenic sodium pump in cardiac Purkinje fibres

“…Cooling can increase internal Na activity, [Na]i, by decreasing Na pump activity. On rewarming the tissue following such hypothermia, the resting potential transiently overshoots the control level to more negative potentials (Page & Storm, 1965;Tamai & Kagiyama, 1968;Hiraoka & Hecht, 1973;Glitsch, Grabowski & Thielen, 1978). Alternatively [Na]i can be raised by blocking the Na pump by exposing the tissue to K-depleted solutions (Noma & Irisawa, 1975;Ellis, 1977).…”