Developmental changes in isolated rat type I carotid body cell K+ currents and their modulation by hypoxia

1. Whole-cell patch-clamp recordings were used to investigate possible age-related changes in K+ currents of type I carotid body cells isolated from the rat. K+ current density increased with age, as measured in cells isolated from 4-day-old, 10-day-old and adult rats (greater than or equal to 5 weeks old). 2. The proportion of current reversibly inhibited by high [Mg2+] (6 mM), low [Ca2+] (0.1 mM) solutions, indicative of the proportion of current attributable to activation of Ca2+-sensitive K+ (K-Ca) channels, was significantly smaller in cells of 4-day-old rats compared with 10-day-old rats, despite inward Ca2+ current densities being similar in these two age groups. Inhibition of K+ currents by high [Mg2+], low [Ca2+] solutions was similar in 10-day-old and adult type I cells. 3. Hypoxia (P-O2, 16-23 mmHg) caused reversible reductions in type I cells from rats of all age groups. However, reductions seen in cells of 4-day-old rats were significantly smaller than those seen in cells of 10-day-olds and adults. The degree of hypoxic inhibition in these latter two groups was not significantly different. 4. In the presence of high [Mg2+], low [Ca2+] solutions, hypoxia (P-O2 16-23 mmHg) was without significant effect on residual K+ currents in cells from all age groups. 5. These observations indicate that K+ current density increases with postnatal age in the rat. Between days 4 and 10, there appears to be a predominant enhancement of K-Ca channels, and over the same age range hypoxic sensitivity of K+ currents increases. Our findings demonstrate that this latter observation arises because hypoxia selectively inhibits K-Ca channels in cells at all ages studied. These results suggest an important role for K-Ca channels in postnatal maturation of hypoxic chemoreception in the rat carotid body.