The ‘sodium pump lag’ revisited

Effects of amiloride in guinea‐pig and rat left atrial contraction as affected by frequency of stimulation and [Ca2+]0‐[Na+]0 ratio: role of Na+/Ca2+exchange

“…Ca2+ from the cells are responsible for the differences in contractile behaviour, with respect to the parameters of stimulation, existing between both atrial and ventricular myocardium and cardiac muscle from rat and other mammalian species (Sutko et al, 1986). Rat cardiac muscle has some anomalous features (Noble & Powell, 1985); its contractility is less dependent on external [Ca2"] than that of other mammalian species (Willerson et al, 1978;Sutko & Willerson, 1980;Mitchell et al, 1984); its force of contraction does not demonstrate positive staircase in the range of high rates, but increases as the rate of stimulation is decreased (Langer, 1983;Orchard & Lakatta, 1985;Stemmer & Akera, 1986). At the low-frequency end of the frequency-strength curve, guinea-pig left atria exhibits similar behaviour (Blinks & Koch-Weser, 1961;Gibbons, 1986).…”

Na/Ca exchange and tension development in vascular smooth muscle: effect of amiloride

“…In cardiac muscle this carrier system, which countertransports Ca for Na across the cell membrane, is thought to play an important role in cellular calcium homeostasis and hence in the regulation of contractility (Glitsch et al, 1970;Mullins, 1977;Reuter, 1982;Langer, 1983;Lee, 1985). It has been shown, in cardiac muscle and squid axon, that the Na/Ca exchange system can move calcium in either direction across the cell membrane in exchange for sodium.…”

“…The potassium-sparing diuretic amiloride, a well known inhibitor of two Na transport mechanisms in various tissues, namely a conductive Na entry pathway and a Na/H exchange system (Benos, 1982), has recently been found to inhibit the Na/Ca exchange in plasma membrane vesicles from various types of preparations (Smith et al, 1982;Schellenberg et al, 1983;Floreani & Luciani, 1984;Luciani & Floreani, 1985;Debetto et al, 1987). In cardiac muscle this carrier system, which countertransports Ca for Na across the cell membrane, is thought to play an important role in cellular calcium homeostasis and hence in the regulation of contractility (Glitsch et al, 1970;Mullins, 1977;Reuter, 1982;Langer, 1983;Lee, 1985). It has been shown, in cardiac muscle and squid axon, that the Na/Ca exchange system can move calcium in either direction across the cell membrane in exchange for sodium.…”

Optical measurement of voltage-dependent Ca2+ influx in frog heart.

“…The small Ca2+ fluxes observed after inactivation of Ca2+ current tend to exclude major contributions to the influx of Ca2+ from other sarcolemmal Ca2+ transport mechanisms-e.g., Na-Ca exchange. To test this point further, we compared the effects of different inotropic agents of which two, epinephrine and diltiazem, are known to alter the Ca2+ current, while the others, strophanthidin and K +-poor solutions, are thought to act by enhancing the transport of Ca2+ through Na-Ca countertransport systems (22)(23)(24). We found that epinephrine (Fig.…”