ISSN:
1432-1424
Keywords:
Distal nephron
;
Stretch-activated channel
;
Nonselective cation channel
;
Patch clamp study
;
Cytosolic free Ca2+
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract To characterize the Ca2+ transport process across the apical membrane of the rabbit connecting tubule (CNT), we examined the effects of luminal pressure on parathyroid hormone (PTH)-dependent apical Ca2+ transport in this segment perfused in vitro. An increase of perfusion pressure (0.2 to 1.2 KPa) caused cytoplasmic free Ca2+ concentration ([Ca2+].) to increase by 42 ± 11 nm in Fura-2 loaded perfused CNT. The response was accentuated when 10 nm PTH was added to the bath (101 ± 30 nm, n = 6). Addition of 0.1 mm chlorphenylthio-cAMP (CPT-cAMP) to the bath also augmented the [Ca2+]; response to pressure from 36 ± 16 to 84 ± 26 nm (n = 3). Under steady perfusion pressure at 1.2 KPa, PTH (10 nm) increased [Ca2+]; by 31 ± 7 nm (n = 5), whereas it did only slightly by 6 ± 2 nm (n = 12) at 0.2 KPa. The pressure-dependent increase of [Ca2+]; was abolished by removing luminal Ca2+ (n = 3), and was not affected by 0.1 and 10 μm nicardipine (n = 4) in the presence of 10 nm PTH. Cell-attached patch clamp studies on the apical membrane of everted CNT with pipettes filled with either 200 mm CaCl2 or 140 mm NaCl revealed channel activities with conductances of 42 ± 2 pS (n = 4) or 173 ± 7 pS (n = 5), respectively. An application of negative pressure (−4.9 KPa) to the patch pipette augmented its mean number of open channels (NP 0 ) from 0.005 ± 0.001 to 0.022 ± 0.005 in the Ca2+-filled pipette, and was further accelerated to 0.085 ± 0.014 (n = 3) by 0.1 mm CPT-cAMP. In the Na+-filled pipette, similar results were obtained (n = 3), and CPT-cAMP did not activate the stretch-activated channel in the absence of negative pressure (n = 3). These results suggest that a stretch-activated nonselective cation channel exists in the apical membrane of the CNT and that it is activated by PTH in the presence of hydrostatic pressure, allowing entry of Ca2+ transport from the apical membrane.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00232900
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