Intracellular potassium and sodium activities of chick ventricular muscle during embryonic development.

Abstract

SUMMARY1. The basis of the resting potential of chick embryo ventricular muscle was studied by use of ion-selective micro-electrodes. Membrane resting potential hyperpolarized from -65-4 + 1-1 mV (mean + s.E.) at age 4 day to ---75-8 + 0-6 mV at age 18 day. Action potential overshoot increased from + 19-8 + 0-9 at age 4 day to +33-1+0-6mVatage 18 day.2., Intracellular K+ activity measured with ion-selective micro-electrodes increased from 71-3 + 1-9 mm at age 4 day to 89-9 + 1-1 mM at age 18 day. Intracellular Na+ activity decreased from 12-5 + 0-4 to 7-0 + 0-3 mm during the same period. The difference between membrane resting potential and the calculated potassium equilibrium potential decreased with development. PNa/PK estimated from the constant field equation decreased from 0-012 at age 4 day to 0-005 at age 18 day.3. The hyperpolarization of resting potential and the increased action potential overshoot during development could be explained by a rise in intracellular K+ activity and a fall in intracellular Na+ activity, as if the Na-K exchange pump became more active.

Calcium signalling in developing cardiomyocytes: implications for model systems and disease

“…Based on these data, mathematical modelling suggested a role for NCX-triggered Ca 2+ release at these sites. In both diseased and developing cells, lower expression of the Na + -K + ATPase, particularly the α2 isoform, is associated with elevated intracellular Na + levels, which favours the Ca 2+ entry mode of NCX function (Fozzard & Sheu, 1980;Herrera et al 1994;Artman et al 2000;Swift et al 2008;Louch et al 2010a;Li et al 2012).…”

Surface charge near the cardiac inward-rectifier channel measured from single-channel conductance

“…The conductance (in this case, ARs) strongly rectifies, passing current only when the transmembrane potential is negative to the K reversal potential. Reversal lies close to zero mV because the pipette contains 100 mM K, about equal to the free K in 7 + 1 day embryonic ventricular cells [83 mM by ionselective electrodes (Fozzard & Sheu, 1980) and 138 mM by flame photometry (McDonald & DeHaan, 1973). Figure 2 gives the i(V) curve for Fig.…”

Intracellular potassium activity in rabbit sinoatrial node. Evaluation during spontaneous activity and arrest.

“…We conclude that (1) ak is similar in the sinoatrial node and right atrium, (2) the slow frequency response of the ion sensitive microelectrode may lead to a considerable overestimate of ak, (3) the low MDP in SA nodal cells compared with the atrium is not the result of a low ak, and (4) the net driving force on potassium ions is outward throughout the range of pacemaker potentials at normal [K + ] o . (C/rc Res 51: [271][272][273][274][275][276][277][278][279]1982) MEASUREMENTS of the transmembrane distribution of K + with ion-sensitive microelectrodes have confirmed that the distribution of K + is largely responsible for the maximum diastolic and resting potentials in Purkinje fibers and working myocardium (Walker and Ladle, 1973;Lee and Fozzard, 1975;Fozzard and Lee, 1976;Miura et al 1977;Fozzard and Sheu, 1980). Maximum diastolic and resting potentials of sinoatrial (SA) and atrioventricular (AV) nodal cells are much lower (Irisawa, 1978;Sperelakis, 1979).…”