HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Jiang, Z.-G. Articles by Nuttall, A. L. Search for Related Content PubMed PubMed Citation Articles by Jiang, Z.-G. Articles by Nuttall, A. L.

Two resting potential levels regulated by the inward-rectifier potassium channel in the guinea-pig spiral modiolar artery

Zhi-Gen Jiang *, Jun-Qiang Si *†, Michael R. Lasarev ‡ and Alfred L. Nuttall *§

1. Intracellular in vitro recordings were made from 771 cells from the spiral modiolar artery (SMA). The initial resting potentials (RPs) displayed a bimodal distribution that was well modelled as a mixture of two Gaussian distributions. About half of the cells had an average RP of -74 mV, and were termed high-RP cells, whereas the other half had an average RP around -41 mV, and were termed low-RP cells. Preparations that were incubated for longer than 24 h contained significantly more high-RP cells than those incubated for less than 8 h.
2. When labelled with the fluorescent dye propidium iodide, 68 and 36 cells were identified as smooth muscle cells (SMC) and endothelial cells (EC), respectively. The RP and input resistance were not significantly different between these two types of cell. Dye coupling was observed only in ECs. Dual cell recordings with 0.2-1.0 mm separation demonstrated the simultaneous existence of high- and low-RP cells and a heterogeneous low-strength electrical coupling.
3. The high-RP cells were depolarized by ACh and by high extracellular potassium concentration (high K⁺). The low-RP cells were usually hyperpolarized by moderately high K⁺ (7.5-20 mM) and by ACh. The high K⁺-induced hyperpolarization was suppressed by barium (Ba²⁺, 10-50 µM). The putative gap junction blocker 18-glycyrrhetinic acid suppressed the ACh-induced responses in SMCs, but not in ECs.
4. Low-RP cells could rapidly shift the membrane potential to a permanent high-RP state spontaneously or, more often, after a brief application of hyperpolarizing agents including high K⁺, ACh, nitric oxide and pinacidil. Once shifted to a high-RP state, the responses of these cells to high K⁺ and ACh became similar to those of the original high-RP cells.
5. High-RP cells occasionally shifted their potentials to a low-RP state either spontaneously or after a brief application of 10-50 µM Ba²⁺ or 100 µM ouabain. Once shifted to the low-RP state, the response of these cells to high K⁺ and ACh became a hyperpolarization. The shift between high- and low-RP states was largely mimicked by wash-in and wash-out of low concentrations of Ba²⁺. The shift often showed a regenerative process as a fast phase in its middle course.
6. It is concluded that the cochlear SMA in vitro is composed of poorly and heterogeneously coupled SMCs and ECs, simultaneously resting in one of two distinct states, one a high-RP state and the other a low-RP state. The two RP states are exchangeable mainly due to all-or-none-like conductance changes of the inward-rectifier K⁺ channel.

This article has been cited by other articles:

				C. E. Hill Inward rectification and vascular function: As it was in the beginning J. Physiol., March 15, 2008; 586(6): 1465 - 1467. [Full Text] [PDF]

				Z.-G. Jiang, X.-R. Shi, B.-C. Guan, H. Zhao, and Y.-Q. Yang Dihydropyridines Inhibit Acetylcholine-Induced Hyperpolarization in Cochlear Artery via Blockade of Intermediate-Conductance Calcium-Activated Potassium Channels J. Pharmacol. Exp. Ther., February 1, 2007; 320(2): 544 - 551. [Abstract] [Full Text] [PDF]

				M. A. Machingal and S. V. Ramanan A Steady-State Electrochemical Model of Vascular Smooth Muscle Cells Biophys. J., September 1, 2006; 91(5): 1648 - 1662. [Abstract] [Full Text] [PDF]

				Z.-G. Jiang, A. L Nuttall, H. Zhao, C.-F. Dai, B.-C. Guan, J.-Q. Si, and Y.-Q. Yang Electrical coupling and release of K+ from endothelial cells co-mediate ACh-induced smooth muscle hyperpolarization in guinea-pig inner ear artery J. Physiol., April 15, 2005; 564(2): 475 - 487. [Abstract] [Full Text] [PDF]

				G. H. Seol, S. C. Ahn, J. A. Kim, B. Nilius, and S. H. Suh Inhibition of endothelium-dependent vasorelaxation by extracellular K+: a novel controlling signal for vascular contractility Am J Physiol Heart Circ Physiol, January 1, 2004; 286(1): H329 - H339. [Abstract] [Full Text] [PDF]