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Expression of carotid body muscarinic receptors in developing cats

Cholinergic muscarinic system is involved in chemoreceptor activity, however the developmental pattern of M1 and M2 muscarinic receptors (R) in the carotid body (CB) has not been assessed. Using real time RT‐PCR, northern and western blots analyses, M1 and M2 receptors as well as tyrosine hydroxylase (TH, rate limiting enzyme for dopamine synthesis) mRNA and protein levels were evaluated in the CB of 1 and 15 day‐old, 2 month‐old and adult cats. M1R mRNA significant increased by 100% and 300% in 2 month‐old and adult cats vs. 1 and 15 day‐old, but protein decreased 50% at these ages vs. 1 and 15 day‐old. Expression level of M2R mRNA or protein did not changed. TH mRNA and protein levels decreased gradually with age. TH protein levels were 35%, 45% and 53% lower at 15 days, 2 months and in adult cats vs. 1‐day‐old, respectively. Hence, since M1 is involved in the chemosensory activity while the M2 in the regulation of acetylcholine and dopamine release from chemosensitive cells, this pattern of age dependent expression levels of M1 and M2 R in cat CB suggests that the physiological role of these receptors on CB function changes with age.