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TMEM16A: A Candidate for Calcium-Activated Chloride Channels in Smooth Muscle Vasculature Background: Calcium-activated chloride channels (CaCCs) play a major role in vascular smooth muscle excitability. Yet, the molecular identity of the underlying channel protein remains elusive. CLCA and bestrophin genes have been proposed as candidates for CaCCs but currents generated by the overexpression of these genes lack some of the characteristics of native CaCC currents. Recently a new gene has been identified, TMEM16A, which when expressed produces currents displaying biophysical properties similar to native calcium-activated chloride currents (IClCa) (Yang et al, 2008; Caputo et al, 2008; Schroeder et al, 2008). The aim was to determine if TMEM16A & B was expressed in vascular smooth muscle so it could be considered a molecular correlate for CaCCs.
Methods: Whole-cell patch clamp electrophysiological recordings, reverse transcriptase polymerase chain reaction (RT-PCR) and immunological experiments were performed on various murine (BALB/c; 6 – 8 weeks) blood vessels or isolated smooth muscle cells.
Results: Cl- currents with distinctive voltage-dependent characteristics were recorded from myocytes isolated from murine portal vein, aorta and carotid artery cells (n≥5). TMEM16A gene expression was detected in all smooth muscle samples tested (n=3). In contrast, the expression of the closely related gene, TMEM16B, was more varied (n=3). Protein expression was detected by two different TMEM16A antibodies and was shown to localise to the smooth muscle layer in various blood vessels by immunohistochemistry (n≥3) and immunocytochemistry (n≥3).
Conclusion: This qualitative study is the first to demonstrate the presence of TMEM16A mRNA and protein in a variety of vascular smooth muscle tissues. TMEM16A can now be considered a strong candidate for calcium-activated chloride channels in smooth muscle vasculature.
Yang et al, (2008). Nature 455:1210-5. |
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