CHANGES IN MEMBRANE CONDUCTANCE BY MECHANICAL STRETCH IN RABBIT SINOATRIAL NODE CELLS

We investigated the effects of membrane stretch on the membrane conduc tance in rabbit sinoatrial (SA) node cells using the whole-cell voltag e-clamp method. The Cl- current was activated by both osmotic cell swe lling and the cell inflation method under conditions where other time- dependent currents were blocked by applying appropriate blockers as al ready described in the literature. On the other hand, the time-depende nt calcium current was also increased by membrane stretch in SA node c ells. The L-type calcium current (I-Ca,I-L) was reversibly increased b y 35% by applying positive pressure through the patch pipette or by os motic cell swelling in the presence of 2 mM Ca2+ or 2 mM Ba2+. The kin etic properties of I-Ca,I-L were unchanged by the membrane stretching. The increase in I-Ca,I-L occurred in the presence of protein kinase i nhibitors. These results suggested that membrane stretch might directl y modulate I-ca,I-L through a phosphorylation-independent process. The present increase of I-Ca,I-L, together with activation of the stretch -activated Cl- current may partly contribute to the positive chronotro pic effect seen during membrane stretch in SA node cells.