Adenovirus-Mediated Expression of Sense and Antisense Connexins Alters Gap Junctional Conductance and the Burst Period of Electrical Activity in Mouse Pancreatic Islets
Abstract Number: 95-OR
Authors: MIN ZHANG, ARTHUR SHERMAN, LESLIE SATIN
Institutions: Richmond, VA; Bethesda, MD
Results: Beta cells within the islet are electrically coupled via connexin-mediated gap junctions, which is responsible for synchronizing electrical activity across the islet. Simulations demonstrate that altering gap junctional conductance (Gc) can profoundly affect the period of electrical bursting; in some models, slower oscillations require an optimal level of Gc, with values below and above this optimum resulting in faster activity. We systematically modulated Gc in cultured mouse islets using adenovirus constructs (AdVs) to alter connexin expression. Gc was estimated by recording ionic currents and membrane potentials due to bursting in superficial islet cells using the patch clamp. In control islets cultured for 1-2 days, mean Gc was 0.75 +/- .097 nS (N=7). Exposing islets to AdV constructs containing Cx 36 or Cx 43 in the antisense orientation reduced Gc to 0.19+/- 0.07 nS (N=12) or 0.29 +/- nS 0.06(N=10), respectively (p<0.001; p<0.001). Overexpressing Cx 36 or Cx 43 increased Gc to 1.89+/- 0.37 nS (N=7) and 2.32 +/- nS 0.22 (N=8), respectively (p<0.05; p<0.0007). Controls for AdV exposure did not differ from naïve controls. Islets showing the slowest oscillations had Gc values near 0.75 nS; above or below this optimum resulted in faster bursting. Thus, islets treated with AdV-Cx 36AS or Cx 43AS had faster than normal bursting and a paucity of slow (i.e. period about 200 s) oscillations, while islets treated with AdV-Cx36S or Cx43S were also primarily fast, despite their larger Gc values. These results suggest that Cx 36 and Cx 43 may both contribute to electrical coupling in mouse islets, and that Gc is an important predictor of the period of electrical oscillations. This is the first experimental evidence in support of the theoretical prediction that an optimum degree of coupling is required for slow oscillations in islets. This may in part account for the different electrical behavior of islets vs. dispersed single beta cells.