Contribution of reverse Na + –Ca 2+ exchange to spontaneous activity in interstitial cells of Cajal in the rabbit urethra

Bradley, Eamonn and Hollywood, Mark A. and Johnston, Louise and Large, Roddy J. and Matsuda, T and Baba, A. and McHale, Noel G. and Thornbury, Keith D. and Sergeant, Gerard P. (2006) Contribution of reverse Na + –Ca 2+ exchange to spontaneous activity in interstitial cells of Cajal in the rabbit urethra. The Journal of Physiology, 574 (3). pp. 651-661.

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Interstitial cells of Cajal (ICC) isolated from the rabbit urethra exhibit regular Ca 2+ oscillations that are associated with spontaneous transient inward currents (STICs) recorded under voltage clamp. Their frequency is known to be very sensitive to external Ca 2+ concentration but the mechanism of this has yet to be elucidated. In the present study experiments were performed to assess the role of Na + –Ca 2+ exchange (NCX) in this process. Membrane currents were recorded using the patch clamp technique and measurements of intracellular Ca 2+ were made using fast confocal microscopy. When reverse mode NCX was enhanced by decreasing the external Na + concentration [Na + ] o from 130 to 13 mM, the frequency of global Ca 2+ oscillations and STICs increased. Conversely, inhibition of reverse mode NCX by KB-R7943 and SEA0400 decreased the frequency of Ca 2+ oscillations and STICs. Application of caffeine (10 mM) and noradrenaline (10 μM) induced transient Ca 2+ -activated chloride currents (I ClCa ) at −60 mV due to release of Ca 2+ from ryanodine- and inositol trisphosphate (IP 3 )-sensitive Ca 2+ stores, respectively, but these responses were not blocked by KB-R7943 or SEA0400 suggesting that neither drug blocked Ca 2+ -activated chloride channels or Ca 2+ release from stores. Intact strips of rabbit urethra smooth muscle develop spontaneous myogenic tone. This tone was relaxed by application of SEA0400 in a concentration-dependent fashion. Finally, single cell RT-PCR experiments revealed that isolated ICC from the rabbit urethra only express the type 3 isoform of the Na + –Ca 2+ exchanger (NCX3). These results suggest that frequency of spontaneous activity in urethral ICC can be modulated by Ca 2+ entry via reverse NCX.

Item Type: Article
Uncontrolled Keywords: Muscle, smooth; Interstitial cells of Cajal; Rabbit; Urethra; Patch clamp technique
Subjects: Science
Research Centres: Smooth Muscle Research Centre
Depositing User: Concepta Woods
Date Deposited: 26 Nov 2011 12:59
Last Modified: 11 Nov 2014 16:10

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