Ion channels in rabbit cultured fibroblasts

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Abstract
Large outward currents are recorded with the whole-cell patch-clamp technique on depolarization of rabbit cultured fibroblasts. Our findings suggest that these outward currents consist of two voltage-dependent components, one of which also depends on cytoplasmic calcium concentration. Total replacement of external Cl$^{-}$ by the large anion ascorbate does not affect the amplitude of the currents, indicating that both components must be carried by K$^{+}$. Consistent with these findings with whole-cell currents, in single channel recordings from fibroblasts we found that most patches contain high-conductance potassium-selective channels whose activation depends on both membrane potential and the calcium concentration at the cytoplasmic surface of the membrane. In a smaller number of patches, a second population of high-conductance calcium-independent potassium channels is observed having different voltage-dependence. The calcium-and voltage-dependence suggest that these two channels correspond with the two components of outward current seen in the whole-cell recordings. The single channel conductance of both channels in symmetrical KCl (150 mM) is 260-270 pS. Both channels are highly selective for K$^{+}$ over both Na$^{+}$ and Cl$^{-}$. The conductance of the channels when outward current is carried by Rb$^{+}$ is considerably smaller than when it is carried by K$^{+}$. Some evidence is adduced to support the hypothesis that these potassium channel populations may be involved in the control of cell proliferation.