Both hypoxic preconditioning (HP) and chronic hypoxia (CH) protect the heart against injury caused by acute oxygen deprivation. The aim was to find out whether the large conductance K⁺ channel (BK_Ca) is involved in the protection of ventricular myocytes isolated from HP and CH rats. Animals were exposed to continuous normobaric hypoxia (10% O₂) for 24 h (HP) or 21 days (CH) followed by 24 h of normoxia, or kept at room air (normoxic group). Myocytes were isolated from the left ventricular free wall and subjected to either no addition (control), DMSO (solvent control), 30 mM NS1619 (BK_Ca-opener) or 2 mM paxilline (BK_Ca-blocker) 25 min prior to and during the experiment. Afterwards, myocytes were subjected to 25 min of "anoxia" (metabolic inhibition) followed by 30 min of reoxygenation (A/R). Viability and LDH release were evaluated at the beginning of the experiment, after anoxia, and after reoxygenation. Initial cell viability and LDH (total and released) did not differ among the groups. A/R decreased viability of untreated and DMSO-treated myocytes from normoxic rats to 44% and 31% of pre-anoxic values, respectively. HP and CH increased viability to 79% and 65%, respectively. While NS1619 significantly increased the number of surviving myocytes from the normoxic group (75%), it had no additional effect in HP and CH groups (86% and 77%, respectively). Paxilline significantly attenuated the protective effect of HP and CH but viability was still higher (58% and 49%, respectively) compared with the normoxic group. Similar protective effects were observed when LDH release was measured. LDH release after A/R was significantly lower in HP (110% of preanoxic value) compared with normoxic controls (140%) while the protection afforded by CH was slightly less pronounced (116%). NS1619 reduced LDH release in the normoxic group (109%) but not in HP and CH groups (112% and 113%, respectively). On the other hand, paxilline significantly attenuated protective effects of HP and CH (128% both) without affecting LDH release in the normoxic group (135%). It is concluded that BKCa channels contribute to the improved tolerance to acute A/R injury of myocytes isolated from hearts of preconditioned and chronically hypoxic rats.

Supported by GA CR 305/07/0875, 305/07/1008 and IAA500110804