Hypoosmotic cell swelling as a novel mechanism for modulation of cloned HCN2 channels
Kirstine Calloe 1*, Pernille Elmedyb 1, Soren-Peter Olesen 1, Nanna Koschmieder Jorgensen 1 and Morten Grunnet 2
1 The Panum Institute
2 NeuroSearch A/S
* To whom correspondence should be addressed. E-mail: kirstinec{at}mfi.ku.dk.
Submitted on March 30, 2005
Revised on May 13, 2005
Accepted on 14 June 2005
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Abstract |
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The present work demonstrates activation by cell swelling as a new regulatory mechanism for the cloned Hyperpolarization-activated, Cyclic Nucleotide-gated channel 2 (HCN2). HCN2 channels were co-expressed with aquaporin 1 (AQP1) in Xenopus laevis oocytes and currents were monitored using two-electrode voltage-clamp. HCN2 channels were activated by hyperpolarization to - 100 mV and the currents were measured before and after the oocytes were subjected to hypoosmotic cell swelling. Cell swelling increased HCN2 currents by 30 % without changing the kinetics of the currents. Injection of 50.6 nl isoosmotic solution resulted in a current increase by 20 %, indicating that an increase in cell volume also under isoosmotic conditions may lead to activation of HCN2. In the absence of AQP1 only negligible changes in oocyte cell volume occur during exposure to hypoosmotic media and no significant change in HCN2 channel activity was observed during perfusion with hypoosmotic media. This indicates that cell swelling and not a change in ionic strength of the media, caused the observed swelling-induced increase in current. The increase in HCN2 current induced by cell swelling could be abolished by Cytochalasin D (CD) treatment, indicating that an intact F-actin cytoskeleton is a prerequisite for the swelling-induced activation.
Key Words:
HCN2, Hyperpolarization-activated cyclic nucleotide-gated channel, Hypoosmotic swelling, Xenopus laevis oocytes, electrophysiology, ion channels
