THE EFFECT OF Na, K AND CIIONS ON THE RESTING MEMBRANE POTENTIAL OF SINOATRIAL NODE CELL OF THE RABBIT

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Abstract
The resting membrane potential of S-A [sino-atrial] node cell was investigated by observing the response of the membrane potential to change in [K+]o or [Cl-]o under the presence or absence of Na+. The slope of the change in membrane potential per decade change in [K+]o increased from 12.3-44 mV by removal of Na+ from the external medium, suggesting an extensive contribution of Na+ to the resting membrane potential. To determine the relative conductance between Na and K ions, Cl- in Tyrode solution was substituted with SCN-, which is 2.1 times more permeable than Cl-, in order to eliminate the contribution of Cl concentration cell to the resting membrane potential. The contribution of the Cl- to the resting membrane potential could be examined only in Na-free medium. Acetate ion was reported to be 0.5 times less permeable than Cl-. The replacement of Cl- by acetate ion in various proportions caused a transient depolarization. The slope of this transient depolarization per decade change of [Cl-]o between 10-100 mM was determined to be -6.8 mV. Under the assumption that the resting membrane potential could be determined by the parallel concentration cells for Na, K and Cl, relative conductance ratio between K, Na and Cl was calculated to be 1:0.58:0.15.