Pre‐junctional potentiation of ATP overflow is age‐dependent

Abstract

The purpose was to evaluate the role of α2‐pre‐junctional receptors in ATP overflow in the resistance arterioles from adult and middle aged rats. Using F344 rats (6 months old: n=5 female; n=6 males) and (12 months old: n=5 females; n=5 males), the 1A arterioles from the red gastrocnemius muscle were dissected and cannulated with glass pipettes in a tissue bath. The ATP and null probes were positioned such that the tips of the probes were touching the arteriole in similar anatomical locations and a normal ATP curve was generated (0.78μM to 25 μM ATP). Field stimulation resulted in an increase in ATP overflow in arterioles from 6‐month old rats (1.88±6.14 μM ATP) and 12‐month old rats (34.95±91.30 μM ATP). Adding the α2‐agonist, UK14,304, resulted in no change in 6‐month olds (3.34±3.10 μM ATP), but increased ATP overflow in some 12‐month olds (119.09±256.71 μM). Blocking α2‐receptors using idozoxan, had little effect on 6‐month olds (1.81±1.59 μM ATP), but blocked the action of UK14,304 in 12‐month olds (11.74±23.04 μM ATP). There were no sex‐related differences in ATP overflow. These data indicate that there are significant age‐related changes in mechanisms modulating ATP overflow in skeletal muscle resistance vessels and that α2‐pre‐junctional activation may not act in the way previously described in the heart, brain and tail. This research was supported by NIA (R03AG033245) and the Arkansas Biosciences Institute.