Biphasic effects of cell volume on excitation-contraction coupling in rabbit ventricular myocytes.
We studied the effects of osmotic swelling on the components of excitation-contraction coupling in ventricular myocytes. Myocyte volume rapidly increased 30% in hyposmotic (0.6T) solution and was constant thereafter. Cell shortening transiently increased 31% after 4 min in 0.6T but then decreased to 68% of control after 20 min. In parallel, the L-type Ca(2+) current (I(Ca-L)) transiently increased 10% and then declined to 70% of control. Similar biphasic effects on shortening were observed under current clamp. In contrast, action potential duration was unchanged at 4 min but decreased to 72% of control after 20 min. Ca(2+) transients were measured with fura 2-AM. The emission ratio with excitation at 340 and 380 nm (f(340)/f(380)) decreased by 12% after 3 min in 0.6T, whereas shortening and I(Ca-L) increased at the same time. After 8 min, shortening, I(Ca-L), and the f(340)/f(380) ratio decreased 28, 25, and 59%, respectively. The results suggest that osmotic swelling causes biphasic changes in I(Ca-L) that contribute to its biphasic effects on contraction. In addition, swelling initially appears to reduce the Ca(2+) transient initiated by a given I(Ca-L), and later, both I(Ca-L) and the Ca(2+) transient are inhibited.
Li
Gui-Rong
GR
Department of Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
Zhang
Min
M
Satin
Leslie S
LS
Baumgarten
Clive M
CM
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D020746:Calcium Channels, L-Type / Q000502:physiology; D048429:Cell Size / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles; D007700:Kinetics; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology*; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D011817:Rabbits; D013997:Time Factors
D020746:Calcium Channels, L-Type