Eicosanoids modulate apical Ca(2+)-dependent K+ channels in cultured rabbit principal cells

Abstract

Patch clamp technology was utilized to study the effects of apical phospholipase A2 (PLA2) metabolites on "maxi K" channels in the principal cell apical membrane of rabbit cortical collecting tubule (CCT) primary cultures (B. N. Ling, C. F. Hinton, and D. C. Eaton. Kidney Int. 40: 441-452, 1991). At resting membrane potential, this channel is quiescent in the cell-attached configuration. Apical application of the PLA2 agonist melittin (1 microgram/ml) for 10 min increased single-channel open probability (Po) from 0.0004 +/- 0.0010 to 0.11 +/- 0.05. Similarly, apical exposure to 50 microM arachidonic acid (AA) or 0.5 microM prostaglandin (PG) E2, but not 0.5 microM PGF2 alpha, also increased channel activity. Conversely, 10 microM of the PLA2 antagonist quinacrine applied apically decreased Po. Removal of apical bath Ca2+ did not prevent melittin-, AA-, or PGE2-induced channel activation. We then examined the role of maxi K channels and eicosanoids in principal cell volume regulation. Within seconds of reducing basolateral bath tonicity (285 to 214 mosmol/kgH2O), NPo (i.e., no. of channels x Po) initially increased approximately 200%, followed by a delayed but prolonged activation phase that was attenuated by removal of apical bath Ca2+. Pretreatment with 10 microM quinacrine, 100 microM indomethacin (cyclooxygenase inhibitor), or 0.25 microM thapsigargin (to deplete intracellular Ca2+ stores) abolished the initial phase of swelling-induced channel activation.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of calcium channel currents by arachidonic acid in single smooth muscle cells from vas deferens of the guinea‐pig

“…Moreover, the effect of AA was not changed when the Ca2+ concentration in the pipette solution was changed in the pCa range of 7.0 and 10.0 by use of Ca-EGTA buffer, 5 mM EGTA or 15 mM BAPTA. The AA-induced decrease in IBa was, therefore, not modulated by the intracellular calcium concentration, although it is known that AA and its metabolites change Ca2`release from storage sites (Force et al, 1990;Ling et al, 1992;Maruyama, 1993). This suggests that the inactivation of Ca channels by intracellular Ca2`which is increased by Ca2+-influx and Ca2+-release from intracellular Ca storage sites is not involved in the mechanism of AA-induced decrease in Ca channel current.…”

Inhibition of apical Na+ channels in rabbit cortical collecting tubules by basolateral prostaglandin E2 is modulated by protein kinase C.

“…As previously described, kidneys were dissected from New Zealand white rabbits (1-2 kg) in ice-cold Hepes-buffered saline solution containing ( (3,(16)(17)(18). The renal cortex was separated and incubated for 60 minutes at 370C (equilibrated with 4% CO2 in air) in a solution containing: 4 ml of Hepesbuffered saline, 0.25 ml 10% BSA, 6.2 mg ofcollagenase (type I; Sigma Chemical Co., St. Louis, MO), and 4 ml of RK-l medium.…”

“…CCT fragments, contained in the lower part ofthe Percoll Fl separation band, were plated at confluent density on permeable, glutaraldehyde-fixed collagen films attached to the bottoms of small lucite rings (3,15,17,18). This sided preparation allows patch pipette accessto the apical membrane, and separate control of the apical and basolateral bath compositions (Fig.…”

“…This sided preparation allows patch pipette accessto the apical membrane, and separate control of the apical and basolateral bath compositions (Fig. 1 (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) were obtained on principal cell apical membranes, as previously described (3,17,18 When channels were too numerous to clearly distinguish the individual channel current levels by histogram, the amplitude of single channel events were measured from the actual patch clamp recordings. The total number offunctional channels (N) in the patch were preliminarily estimated by observing the number ofpeaks detected on current amplitude histograms.…”

Epoxyeicosatrienoic Acid Activates BK Channels in the Cortical Collecting Duct

“…13 In addition to CYP-epoxygenase, COX and CYP--hydroxylase have been shown to be able to metabolize AA in the renal tubules, including CCD. 28 The COX-dependent AA metabolites such as prostaglandin E 2 have been shown to activate BK channels in cultured rabbit CCD by increasing intracellular Ca 2ϩ release 35 ; however, the observation that inhibition of COX did not abolish the stimulatory effect of AA on BK channels excluded the possibility that the COX-dependent metabolites of AA were responsible for the stimulatory effect of AA on BK channels. Moreover, we previously demonstrated that HK intake suppressed the expression of COX-2 expression in the kidney.…”