Single K⁺ channels in endocrine cells dispersed from the cricket (Gryllus bimaculatus) corpora allata

Abstract.

Single channel currents were recorded from cell-attached patches of endocrine cells of the adult male cricket corpora allata. Three distinct types of K⁺ channels were identified; a weak inward rectifier (Type 1), a strong inward rectifier (Type 2) and a weak outward rectifier (Type 3). The type 1 channel had a slope conductance of 191±9 pS (n=4) at negative membrane potentials (Vm) and 101±6 pS (n=6) at positive Vm. In addition, the channel showed fast open-closed kinetics at negative Vm and slow open-closed kinetics at positive Vm. The open probability (Po) of this channel was strongly voltage-dependent at positive Vm, but less voltage-dependent at negative Vm. The reversal potential was not modified significantly by the substitution of gluconate^– for external Cl^– but was modified after N-methyl-D-glucamine (NMDG⁺) was substituted for external K⁺, according to the Nernst equation for a K⁺-selective channel. The type 2 channel had a slope conductance of 44±2 pS (n=5) at negative Vm, but no detectable outward current was observed at positive Vm. This channel showed very slow open-closed kinetics at negative Vm and its Po was not voltage-dependent. The type 3 channel had a limit conductance of 55±12 pS (n=3) at negative Vm and 88±10 pS (n=3) at positive Vm. This channel showed slow open-closed kinetics at negative Vm and fast open-closed kinetics at positive Vm. The Po for the channel was voltage-dependent at positive Vm but was voltage-independent at negative Vm. These three types of K⁺ channels may be important for the control of the resting membrane potential, and may thus participate in the regulation of Ca²⁺ influx and juvenile hormone secretion in corpora allata cells.