Inward rectifier K channels in renal epithelioid cells (MDCK) activated by serotonin

Abstract

The present study has been performed to test for the effect of intracellular calcium and of serotonin on the channel activity in patches from subconfluent MDCK-cells. In inside-out patches, inwardly rectifying potassium-selective channels are observed with open probabilities of 0.01 +/- 0.01, 0.24 +/- 0.03 and 0.39 +/- 0.07, at 100 nmol/liter, 1 mumol/liter or 10 mumol/liter calcium activity, respectively. The single-channel slope conductance is 34 +/- 2 pS, if the potential difference across the patch (Vp) is zero, and approaches 59 +/- 1 pS, if Vp is -50 mV, cell negative. In the cell-attached mode, little channel activity is observed prior to application of serotonin (open probability = 0.03 +/- 0.03). If 1 mumol/liter serotonin is added to the bath perfusate, the open probability increases rapidly to a peak value of 0.34 +/- 0.04 within 8 sec. In continued presence of the hormone, the open probability declines to approach 0.06 +/- 0.02 within 30 sec. At zero potential difference between pipette and reference in the bath (i.e., the potential difference across the patch is equal to the potential difference across the cell membrane), the single-channel conductance is 59 +/- 4 pS. In conclusion, inwardly rectifying potassium channels have been identified in the cell membrane of subconfluent MDCK-cells, which are activated to a similar extent by increase of intracellular calcium activity to 1 mumol/liter and by extracellular application of 1 mumol/liter serotonin.

Whole-cell and single channel K+ and Cl- currents in epithelial cells of frog skin.

“…The open probability of the channel was on average 0.62 at Vp = 0 and increased with depolarization, but the extent of the voltage dependence was quite variable among experiments. These characteristics are common to K channels found in several epithelial preparations, such as basolateral membranes of turtle colon (Richards and Dawson, 1986), rabbit proximal convoluted (Parent et al, 1988) and straight renal tubules , dogfish rectal gland (Greger, Gogelein, and Schlatter, 1987a), subconfluent MDCK cells (Friedrich, Paulmichl, Kolb, and Lang, 1988;Friedrich et al, 1989), and apical membranes of thick ascending limb of rat kidney (Bleich, Schlatter, and Greger, 1990;Greger, Bleich, and Schlatter, 1990). All these channels exhibit inward rectification, conductances in the range 50--70 pS with high K on both sides of the patch, and, where analyzed, an open time constant of ~ 10 ms, at least two closed time constants, the smaller ~ 1 ms, and a weak increase of the open probability with depolarization.…”

Spontaneously oscillating K+ channel activity in transformed Madin-Darby canine kidney cells.

“…The Ca"2-sensitive K+ channel has to be activated by agonists such as serotonin or minoxidil sulfate which exert their effect via the PKC signalling pathway ( 12,13 were found. Moreover, in ras fibroblasts pretreated with lithium, elevated levels of 1,4,5-inositol-triphosphate were found and bradykinin also caused oscillations of the cell membrane potential.…”

“…Microelectrode studies suggested a Ca" -activated K+ channel (6). Such a channel has been described in nontransformed MDCK cells, too, and its regulation has been studied extensively (12,13). Furthermore, it is known that ras-transformation of fibroblasts leads to the expression of a novel Ca2+-activated K+ current (14).…”

Antagonistic actions of renal dopamine and 5‐ hydroxytryptamine: increase in Na+, K+‐ATPase activity in renal proximal tubules via activation of 5‐HT1A receptors

“…There is evidence, however, that 5-HT, in the kidney, can exert marked effects, namely at the level of vasculature and glomerular and tubular structures. The subtypes of 5-HT receptors identified in the kidney and renal cell lines include the 5-HT2 subtype in renal blood vessels (Janssens & Van Nueten, 1986;Wright & Angus, 1987;Shoji et al, 1989;Blackshear et al, 1991) and the glomerulus (Hamamori et al, 1988;Takuwa et al, 1989), the 5-HTlA subtype in the medullary and cortical tick ascending limb of Henle and distal convoluted tubules (Raymond et al, 1993), the 5-HTlB subtype in OK cells from the opossum kidney (Murphy & Bylund, 1990) and the 5-HTID in MDCK cells from the canine kidney (Frederich et al, 1988). In a recent study in the rat kidney, Ramond et al (1993), employing an immunohistochemical technique, failed to identify the 5-HTlA receptor subtype in the proximal nephron.…”