Glucose-sensitive conductances in rat pancreatic β-cells: contribution to electrical activity

AbstractThe perforated patch technique was used to assess the relative contribution of KATP channel activity, assessed from input conductance (Ginput), and volume-sensitive anion channel activity to the induction of electrical activity in single isolated rat pancreatic β-cells by glucose, 2-ketoisocaproate and tolbutamide. In cells equilibrated in the absence of glucose, the membrane potential was −71 mV and Ginput 3.66 nS. Addition of 8 mM glucose resulted in depolarisation, electrical activity and a reduction in Ginput, reflecting an inhibition of KATP channels. Cells equilibrated in 4 mM glucose had a membrane potential of −59 mV and a Ginput of 0.88 nS. In this case, a rise in glucose concentration to 8–20 mM again resulted in depolarisation and electrical activity, but caused a small increase in Ginput. 2-Ketoisocaproate also evoked electrical activity and an increase in Ginput, whereas electrical activity elicited by addition of tolbutamide was accompanied by reduced Ginput. Increasing the concentration of glucose from 4 to 8–20 mM generated a noisy inward current at −70 mV, reflecting activation of the volume-sensitive anion channel. The mean amplitude of this current was glucose-dependent within the range 4–20 mM. Addition of 2-ketoisocaproate or a 15% hypotonic solution elicited similar increases in inward current. In contrast, addition of tolbutamide failed to induce the inward current. It is concluded that KATP channel activity is most sensitive to glucose within the range 0–4 mM. At higher glucose concentrations effective in generating electrical activity, activation of the volume-sensitive anion channel could contribute towards the nutrient-induced increase in Ginput