Am J Physiol Cell Physiol Journal of Applied Physiology
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Am J Physiol Cell Physiol 280: C303-C308, 2001;
0363-6143/01 $5.00
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Vol. 280, Issue 2, C303-C308, February 2001

State-dependent modification of ATP-sensitive K+ channels by phosphatidylinositol 4,5-bisphosphate

Midori Okamura, Masafumi Kakei, Koutaro Ichinari, Akihiro Miyamura, Naoya Oketani, Nobuyuki Koriyama, and Chuwa Tei

First Department of Internal Medicine, Faculty of Medicine, Kagoshima University, Kagoshima 890-8520, Japan

With inside-out patch recordings in ventricular myocytes from the hearts of guinea pigs, we studied ATP-sensitive K+ (KATP) channels activated by phosphatidylinositol 4,5-bisphosphate (PIP2) with respect to sensitivity to ATP when in either a rundown state (RS) or a non-rundown state (NRS). Rundown of KATP channels was induced by exposure either to ATP-free solution or to ATP-free solution containing 19 µM Ca2+. Exposure of membrane patches to 10 µM PIP2 reactivated channels with both types of rundown. The reactivation by PIP2 did not require ATP in the bath. The IC50 of channels recovered from RS and before the rundown was 37.1 and 31.1 µM, respectively. PIP2 irreversibly increased the mean current when the channel was in the NRS. This was associated with a shift of IC50 to 250.6 µM after PIP2 exposure. PIP2 activates NRS KATP channels by decreasing their sensitivity to ATP, whereas PIP2 reactivates RS-KATP channels independently of ATP without changing ATP sensitivity.

channel rundown; ventricular myocytes


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