MAGNITUDE AND MODULATION OF PANCREATIC BETA-CELL GAP JUNCTION ELECTRICAL CONDUCTANCE IN-SITU

The parallel gap junction electrical conductance between a beta-cell a nd its nearest neighbors was measured by using an intracellular microe lectrode to clamp the voltage of a beta-cell within a bursting islet o f Langerhans. The holding current records consisted of bursts of inwar d current due to the synchronized oscillations in membrane potential o f the surrounding cells. The membrane potential record of the impaled cell, obtained in current clamp mode, was used to estimate the behavio r of the surrounding cells during voltage clamp, and the coupling cond uctance was calculated by dividing the magnitude of the current bursts by that of the voltage bursts. The histogram of coupling conductance magnitude from 26 cells was bimodal with peaks at 2.5 and 3.5 nS, indi cating heterogeneity in extent of electrical communication within the islet of Langerhans. Gap junction conductance reversibly decreased whe n the temperature was lowered from 37 to 30 degrees C and when the ext racellular calcium concentration was raised from 2.56 to 7.56 mM. The coupling conductance decreased slightly during the active phase of the burst. Activation of adenylate cyclase with forskolin (10 mu M) resul ted in an increase in cell-to-cell electrical coupling. We conclude th at beta-cell gap junction conductance can be measured in situ under ne ar physiological conditions. Furthermore, the magnitude and physiologi cal regulation of beta-cell gap junction conductance suggest that inte rcellular electrical communication plays an important role in the func tion of the endocrine pancreas.