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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Gap junction channel activity in short-term cultured human detrusor myocyte cell pairs: gating and unitary conductances

¹Department of Urology, Albert Einstein College of Medicine, Bronx; ²Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York; and ³Wake Forest Institute for Regenerative Medicine, Wake Forest University Baptist Medical Center, Winston-Salem, North Carolina

Submitted 23 January 2006 ; accepted in final form 10 July 2006

Several independent lines of investigation indicate that intercellular communication through gap junctions modulates bladder physiology and, moreover, that altered junctional communication may contribute to detrusor overactivity. However, as far as we are aware, there are still no direct recordings of gap junction-mediated intercellular currents between human or rat detrusor myocytes. Northern and Western blots were used to identify connexin expression in frozen human bladder tissue and short-term cultured human detrusor myocytes. Double whole cell patch (DWCP) recording revealed that human detrusor myocyte cell pairs were well coupled with an average junctional conductance of 6.5 ± 4.6 nS (ranging from 0.1 to 15 nS, n = 22 cell pairs). Macroscopic gap junction channel currents in human detrusor myocytes exhibited voltage dependence similar to homotypic connexin43. The normalized transjunctional conductance-voltage (G_j-V_j) relationship was symmetrical and well described by a two-state Boltzmann relation (G_min 0.33, V₀ = 63.6 mV, Z = 0.117 or equal to 2.95 gating charges), suggestive of a bilateral voltage-gated mechanism. In symmetric 165 mM CsCl, the measured single-channel slope conductance was 120 pS for the fully open channel and 26 pS for the major substate. Occasionally, other subconductance states were also observed. The single-channel mean open time declined with increasing V_j, accounting for the V_j-dependent decline of macroscopic junctional current. Qualitatively similar electrophysiological characteristics were observed in DWCP of freshly isolated rat detrusor myocytes. These data confirm and extend previous observations and are consistent with reports in other smooth muscle cells types in which Cx43-mediated intercellular communication has been identified.

bladder function; intercellular communication; smooth muscle

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