Calcium currents in interstitial cells from the guinea‐pig bladder

OBJECTIVE To determine whether there are inward currents in interstitial cells (IC) isolated from the guinea‐pig detrusor and if so, to characterise them using the patch‐clamp technique and pharmacological agents. MATERIALS AND METHODS Using the whole‐cell patch‐clamp technique, inward currents were...

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Bibliographic Details
Published in:BJU international 2006-06, Vol.97 (6), p.1338-1343
Main Author: McCLOSKEY, KAREN D.
Format: Article
Language:English
Subjects:
Animals
Biological and medical sciences
Calcium Channel Blockers - pharmacology
Calcium Channels - drug effects
Calcium Channels - metabolism
calcium current
Evoked Potentials - physiology
Female
Fundamental and applied biological sciences. Psychology
Guinea Pigs
interstitial cells of Cajal
Male
Medical sciences
Myocytes, Smooth Muscle - drug effects
Myocytes, Smooth Muscle - metabolism
Nephrology. Urinary tract diseases
urinary bladder
Urinary Bladder - metabolism
Vertebrates: urinary system
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Summary:OBJECTIVE To determine whether there are inward currents in interstitial cells (IC) isolated from the guinea‐pig detrusor and if so, to characterise them using the patch‐clamp technique and pharmacological agents. MATERIALS AND METHODS Using the whole‐cell patch‐clamp technique, inward currents were studied in IC enzymatically isolated from the detrusor of the guinea‐pig bladder. Currents were evoked by stepping positively from a holding potential of − 80 mV. RESULTS Outward K+ currents were blocked by Cs+ internal solution to reveal inward currents, which activated at voltages more positive than − 50 mV, peaked at 0 mV, reversed near + 50 mV and were half‐maximally activated at − 27 mV. The inward currents showed voltage‐dependent inactivation and were half‐maximally inactivated at − 36 mV. Fitting the activation and inactivation data with a Boltzmann function revealed a window current between − 40 mV and + 20 mV. The decay of the current evoked at 0 mV could be fitted with a single exponential with a mean time‐constant of 88 ms. Replacing external Ca2+ with Ba2+ significantly increased this to 344 ms. The current amplitude was augmented by Ba2+, and by Bay K 8644. Inward currents were significantly reduced by 1 µm nifedipine, across the voltage range, but the blockade was more effective on the current evoked at 0 mV than that evoked by a step to − 20 mV, perhaps indicating voltage‐dependence of the action of nifedipine or another component of inward current. Increasing the concentration of the drug to 10 µm caused no further significant reduction either at 0 mV or at −20 mV. However, in the presence of 1 µm nifedipine the latter current was significantly reduced by 100 µm Ni2+. Both currents were significantly reduced in Ca2+‐free solution. CONCLUSIONS IC from the guinea‐pig detrusor possess inward currents with typical characteristics of L‐type Ca2+ current. They also have a component of inward Ca2+ current, which was resistant to nifedipine, but sensitive to Ni2+. Further work is needed to characterise the latter conductance.
ISSN:1464-4096
1464-410X
DOI:10.1111/j.1464-410X.2006.06156.x