Three types of ion channels in the cell membrane of mouse fibroblasts.

Patch clamp recordings carried out in the inside-out configuration revealed activity of three kinds of channels: nonselective cation channels, small-conductance K(+) channels, and large-conductance anion channels. The nonselective cation channels did not distinguish between Na(+) and K(+). The unitary conductance of these channels reached 28 pS in a symmetrical concentration of 200 mM NaCl. A lower value of this parameter was recorded for the small-conductance K(+) channels and in a 50-fold gradient of K(+) (200 mM/4 mM) it reached 8 pS. The high selectivity of these channels to potassium was confirmed by the reversal potential (-97 mV), whose value was close to the equilibrium potential for potassium (-100 mV). One of the features of the largeconductance anion channels was high conductance amounting to 493 pS in a symmetrical concentration of 200 mM NaCl. The channels exhibited three subconductance levels. Moreover, an increase in the open probability of the channels at voltages close to zero was observed. The anion selectivity of the channels was low, because the channels were permeable to both Cl(-) and gluconate - a large anion. Research on the calcium dependence revealed that internal calcium activates nonselective cation channels and small-conductance K(+) channels, but not largeconductance anion channels.