Patch-clamp study of the apical membrane of the midgut of Manduca sexta larvae: direct demonstration of endogenous channels and effect of a Bacillus thuringiensis toxin.

The patch-clamp technique was applied to the apical membrane of epithelial midgut cells of a lepidoptera, Manduca sexta L. Access to the apical membrane, the main target site of Bacillus thuringiensis (Bt) toxins, was achieved by using freshly isolated larval midgut preparations mounted onto holding glass pipettes. The epithelial cells retained their functional integrity, as evidenced by the magnitude of intracellular potentials recorded with microelectrodes.

Molecular identity and regulation of renal potassium channels.

K channels are ubiquitous in animal cells, where they are involved in a variety of physiological functions. In epithelial cells of the kidney, K channels are primarily involved in maintaining membrane potential, recycling and secreting K and regulating cell volume. As many renal K channels have now been studied or identified at the molecular level by means of a variety of approaches, including patch-clamp recordings, cDNA cloning and immunohistochemistry, the purpose of this review is to summarize what is presently known about the molecular identity of renal K channels with an emphasis on their regulatory properties.

Two types of K(+) channels at the basolateral membrane of proximal tubule: inhibitory effect of taurine.

The cell-attached configuration of the patch-clamp technique was used to investigate the effects of taurine on the basolateral potassium channels of rabbit proximal convoluted tubule. In the absence of taurine, the previously reported ATP-blockable channel, K(ATP), was observed in 51% of patches. It is characterized by an inwardly rectifying current-voltage curve with an inward slope conductance of 49 +/- 5 pS (n = 15) and an outward slope conductance of 13 +/- 6 pS (n = 15).

Volume regulation and ion transport in renal cells.

Volume regulatory mechanisms are reviewed for both short- and long-term adaptation of renal cells to anisotonic media. Within minutes after exposure to hypotonic solutions a common feature of many renal cells is the increase in plasma membrane potassium and chloride conductances. Although extrusion of intracellular potassium certainly contributes to a regulatory volume decrease, the role of chloride efflux itself is probably modest, given the relatively low intracellular chloride concentration.

Swelling and cAMP on hyperpolarization-activated Cl- conductance in rat Leydig cells.

We have used the whole cell patch-clamp technique to characterize changes in membrane conductance induced by osmotic swelling in mature rat Leydig cells dialyzed with ATP (control cells) or adenosine 3',5'-cyclic monophosphate (cAMP) plus ATP (cAMP cells). A spontaneous current activation occurs in both groups in isosmotic conditions (300/295 mosM in/out). This development is entirely counteracted in control cells and partly inhibited in cAMP cells by exposing them to a hyperosmotic (350 mosM) bath solution, and these currents increase again in a hyposmotic (205 mosM) bath solution.