ISSN:
1432-1424
Keywords:
Regulatory volume decrease
;
Slowly activating K+ channel
;
Vestibular Labyrinth
;
Vibrating probe
;
Micro-Ussing chamber
;
Patch clamp
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract Volume regulation of vestibular dark cells from the gerbilline inner ear in response to a hypoosmotic challenge depends on the presence of cytosolic K+ and Cl−. The present study addresses the questions: (i) whether and by what mechanism K+ is released during volume regulation, (ii) whether the osmolarity of the basolateral medium has an effect on the steady-state rate of transepithelial K+ transport and (iii) whether there is cross-talk between the basolateral membrane responsible for K+ uptake and the apical membrane responsible for K+ release. K+ secretion $$(J_{{\text{K}}^{\text{ + }} ,{\text{probe}}} )$$ and current density (I sc,probe) were measured with vibrating probes in the vicinity of the apical membrane and the transepithelial potential (V t) and resistance (R t) were measured in a micro-Ussing chamber. The equivalent short-circuit current (I sc) was calculated. The current (I IsK), conductance (g IsK) and inactivation time constant (τIsK) of the I sK channel and the apparent reversal potential of the apical membrane (V r) were obtained with the cell-attached macropatch technique. V rwas corrected (V rc) for the membrane voltage (V m) measured separately with microelectrodes. A hypo-osmotic challenge (294 to 154 mosm by removal of 150 mm mannitol) on the basolateral side of the epithelium increased $$J_{K^{\text{ + }} ,{\text{probe}}} $$ and I sc,probe by a factor of 2.7 and 1.6. When this hypo-osmotic challenge was applied to both sides of the epithelium V tand I sc increased from 5 to 14 mV and from 189 to 824 μA/cm2 whereas R tdecreased from 27 to 19 Ω-cm2. With 3.6 mm K+ in the pipette I IsK was outwardly directed, τIsK was 267 msec and the hypo-osmotic challenge caused I IsK and g IsK to increase from 14 to 37 pA and from 292 to 732 pS. V rc hyperpolarized from −44 to −76 mV. With 150 mm K+ in the pipette I IsK was inwardly directed, τIsK was 208 msec and the hypo-osmotic challenge caused I IsK and g IsK to increase in magnitude from 0 to −21 pA and from 107 to 1101 pS. V rc remained unchanged (−2 vs. 1 mV). These data demonstrate that a hypo-osmotic challenge stimulates transepithelial K+ secretion and activates the apical I IsK channel. The hypoosmotically-induced increase in K+ secretion exceeded the estimated amount of K+ release necessary for the maintenance of constant cell volume, suggesting that the rate of basolateral K+ uptake was upregulated in the presence of the hypo-osmotic challenge and that cross-talk exists between the apical membrane and the basolateral membrane.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00234524
