POTASSIUM CHANNELS OF ADULT LOCUST (SCHISTOCERCA-GREGARIA) MUSCLE

Two types of K+ channels have been identified in patches of plasma mem brane of metathoracic extensor tibiae muscle fibres of adult locust, S chistocerca gregaria. One channel had a maximum conductance of 170 pS, fast open-closed kinetics, and a linear current/voltage relationship. In inside-out patches it was activated by ''internally applied'' Ca2, but at unexpectedly low levels (between 10(-10) and 10(-9) M), The o ther channel had a maximum conductance of 35 pS, slower open-closed ki netics, and was not activated by Ca2+ In cell-attached patches, its ch annel conductance measured in symmetrical salines was about three time s greater for hyperpolarisations than for depolarisations. This inward rectification was proved to be due to block by intracellular Mg2+. Fo r both channels, open probability (P-o) and mean open time increased d uring depolarisations and decreased during hyperpolarisations, resulti ng in outward rectifications in terms of net current (I-n, product of the single-channel current and P-o). For both channels, the K+ conduct ance was 10 times greater than that for Na+. Internally applied tetrae thylammonium or tetramethylammonium ions blocked both channels.