Extracellular osmotic pressure modulates sodium-calcium exchange in isolated guinea-pig ventricular myocytes.

1. The sensitivity of the cardiac Na(+)-Ca2+ exchange current to changes in osmotic pressure was investigated in guinea-pig ventricular myocytes, using the whole-cell patch-clamp technique. 2.

Modulation of cardiac L-type Ca2+ channels by GTP gamma S in response to isoprenaline, forskolin and photoreleased nucleotides.

1. Using the patch-clamp recording technique, we have investigated the effects of chronic intracellular application of guanosine thiotriphosphate (GTP gamma S) by cell dialysis, on the potentiation of L-type Ca2+ currents (ICa) by isoprenaline and forskolin and also by GTP gamma S and cyclic AMP released intracellularly by flash-photolysis of their caged derivatives. 2.

The regulation of intracellular Mg2+ in guinea-pig heart, studied with Mg(2+)-selective microelectrodes and fluorochromes.

Because of the reported presence of a Na(+)-Mg2+ exchanger in guinea-pig but not in ferret myocardium, the Mg2+ extrusion mechanism in guinea-pig myocardium has been reinvestigated using Mg(2+)- and Na(+)- selective microelectrodes and the fluorochromes mag-fura-2 and -5. The mean [Mg2+]i measured with microelectrodes in trabeculae or papillary muscles was 0.72 mmol/l (n = 22, thirteen experiments; range 0.

Activation of L-type Ca2+ currents in cardiac myocytes by photoreleased GTP.

L-type calcium currents (ICa) were recorded from isolated ventricular myocytes by using standard patch-clamp methods. In the absence of agonist, photorelease of GTP by flash photolysis of intracellularly applied caged-GTP rapidly increased the amplitude of ICa over a wide range of membrane potentials. Control experiments clearly demonstrated that this effect was not due to either the release of photolytic by-products or to the light flash itself.

Temperature dependence of electrophysiological properties of guinea pig and ground squirrel myocytes.

The effects of changing temperature on the electrophysiology of isolated cardiac myocytes of the guinea pig and Richardson's ground squirrel were studied by patch-clamp techniques. In cells from both species, the resting membrane potential declined on cooling from 36 to 12 degrees C by approximately 6 mV. The duration of the plateau of the action potential in guinea pig cells increased monotonically on cooling.