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The electro physiology of rabbit descending colon 1. instantaneous trans epithelial current voltage relations and the current voltage relations of the sodium entry mechanism


, : The electro physiology of rabbit descending colon 1. instantaneous trans epithelial current voltage relations and the current voltage relations of the sodium entry mechanism. Journal of Membrane Biology 66(1): 41-54

A method is described for determining the instantaneous transepithelial current-voltage (I-V) relations across rabbit descending colon and deriving the I-V relations of the amiloride-sensitive Na-entry step across the apical membrane. The latter conforms closely to the predictions of the Goldman-Hodgkin-Katz constant-field flux equation over a wide range of values of the transapical electrical potential difference (-120 to +50 mV), suggesting that Na entry is the result of simple electrodiffusion through homogeneous pores or channels. The permeability of the apical membrane to Na averaged 0.012 cm/h and the intracellular Na activity averaged 10 mM. The rate of Na entry across the apical membrane varied, spontaneously, over a 4-fold range; this variation is entirely attributable to parallel variations in the partial conductance of the apical membrane to Na with no change in the driving force for this movement. Bathing the serosal surface of the tissue with a high-K solution abolishes the electrical potential difference across the basolateral membrane and markedly reduces the resistance of that barrier. Under these conditions, the I-V relations of the amiloride-sensitive Na-entry step across the apical membrane also conform closely to the predictions of the constant-field flux equation. The significance of the point at which the transepithelial I-V relations in the absence and presence of amiloride intersect (ENa) and the origin of the bends in these I-V relations at or around this point are discussed. The point of intersection is simply that value of the transepithelial electrical potential difference at which Na entry is abolished and has no direct bearing on the energetics of the basolateral pump. The bend in the I-V relations appears to be due to an increase in the conductance of a pathway in the apical membrane that parallels the Na-entry pathway, as well as an increase in the conductance of the paracellular pathway; thus, this bend does not appear to be directly related to changes in the active Na transport pathway.

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Related references

Thompson, S.M.; Suzuki, Y.; Schultz, S.G., 1982: The electrophysiology of rabbit descending colon. I. Instantaneous transepithelial current-voltage relations and the current-voltage relations of the Na-entry mechanism. Journal of Membrane Biology 66(1): 41-54

Thompson, S.M.; Suzuki, Y.; Schultz, S.G., 1982: The electro physiology of rabbit descending colon 2. current voltage relations of the apical membrane the basolateral membrane and the parallel pathways. The data described in the previous paper are employed to derive the current-voltage (I-V) relations of the basolateral membrane, the amiloride-insensitive leak pathway across the apical membrane and the parallel pathways across rabbit descending c...

Turnheim, K.; Thompson, S.M.; Schultz, S.G., 1983: Relation between intracellular sodium and active sodium transport in rabbit colon: current-voltage relations of the apical sodium entry mechanism in the presence of varying luminal sodium concentrations. The current-voltage relations of the amiloride-sensitive Na entry pathway across the apical membrane of rabbit descending colon, exposed to a high K serosal solution, were determined in the presence of varying mucosal Na activities, (Na)m, ranging...

Thomas, S.R.; Suzuki, Y.; Thompson, S.M.; Schultz, S.G., 1983: Electro physiology of necturus maculosus urinary bladder 1. instantaneous current voltage relations in the presence of varying mucosal sodium concentrations. The instantaneous transepithelial current-voltage (I-V) relations of Necturus urinary bladder were determined under short-circuit conditions during impalement of a cell with a microelectrode as described previously (Thompson et al., 1982). These s...

Thompson S.M.; Suzuki Y.; Schultz S.G., 1979: Current voltage relations of the active sodium transport pathway in the rabbit colon. Federation Proceedings 38(3 PART 1): 1061

Thompson, S.M.; Suzuki, Y.; Schultz, S.G., 1982: The electrophysiology of rabbit descending colon. II. Current-voltage relations of the apical membrane, the basolateral membrane, and the parallel pathways. In this paper we employ the data described in the previous paper (I) to derive the current-voltage (I-V) relations of the basolateral membrane, the amiloride-insensitive "leak" pathway across the apical membrane, and the parallel pathway...

Thomas, SR.; Suzuki, Y.; Thompson, SM.; Schultz, SG., 1983: Electrophysiology of Necturus urinary bladder: 1. 'Instantaneous' current-voltage relations in the presence of varying mucosal sodium concentrations. The instantaneous transepithelial current-voltage (I-V) relations of Necturus urinary bladder were determined under short-circuit conditions during impalement of a cell with a microelectrode as described previously (Thompson et al., 1982). These s...

Thomas, S.R.; Suzuki, Y.; Thompson, S.M.; Schultz, S.G., 1983: Electrophysiology of Necturus urinary bladder: I. "Instantaneous" current-voltage relations in the presence of varying mucosal sodium concentrations. The instantaneous transepithelial current-voltage (I-V) relations of Necturus urinary bladder were determined under short-circuit conditions during impalement of a cell with a microelectrode as described previously (Thompson et al., 1982). These s...

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Thompson S.M.; Suzuki Y.; Schultz S.G., 1980: Current voltage relations of the apical and basolateral membranes and shunt pathway of rabbit colon. Federation Proceedings 39(6): ABSTRACT 564