Electrical Characteristics of Suburothelial Cells Isolated From the Human Bladder

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Abstract
We measured the membrane electrical characteristics as well as the response to adenosine triphosphate of cells isolated from the suburothelial layer of the bladder. Suburothelial cells were isolated from biopsy samples of human bladder by collagenase disruption. Electrophysiological measurements were done under current and voltage clamp to record membrane potential and ionic currents using patch pipettes with a K+ based filling solution. Intracellular [Ca2+] was measured with Fura-2. Cells were different from epithelial cells by their spindle-shaped appearance with projections at either end. The cells stained for vimentin but epithelial and smooth muscle cells did not. The cells had small membrane capacitance (27 +/- 16 pF) and a specific membrane resistance of 90 +/- 48 x 10(9) Omega cm2. Average membrane potential was -63 +/- 14 mV but cells showed spontaneous spikes or random fluctuations of membrane potential. A small net inward current was superimposed by a larger outward current. Inward current was attenuated by the removal of extracellular Ca. Outward current showed large spontaneous fluctuations and was greatly decreased by 30 mM tetraethyl ammonium chloride. Adenosine triphosphate (30 to 100 microM) elicited an inward current of about 50 pA and large intracellular Ca2+ transients. These cells are electrically active which, in conjunction with the previous observation of connexin 43 labeling, suggests that they could act as an electrical network. A quantitative model of voltage distribution in such a network after the generation of inward current suggests that individual cells could not act as pacemakers, but rather a group of simultaneously activated cells could exert a peripheral excitatory effect that would amplify the magnitude of the original response. The implications of this in terms of bladder sensation are discussed.