Summation through gap junctions spreads microvascular preconditioning

Brief remote exposure to key agonists preconditions (PC) upstream arterioles, altering local responses (remote microvascular preconditioning, RMP; AJP HC in press 8/26/05). We tested whether RMP could summate to nearby regions. The cheek pouch of anesthetized (Nembutal 70mg/kg) male hamsters (n=31) was observed. The terminal branches of an arteriolar network (NET) were stimulated with nitroprusside (60 s micropipette, NP 10‐4M), initiating both remote dilation, and RMP (op cit). RMP is noted 1000μm away at the entrance to the NET (~12μm dia.) shifting the response to L‐arg (10‐4M) from constrict (−8±5% baseline diameter) to dilate (43±8%). RMP is blocked within NETS by inhibiting gap junctions (micropipette) 18aGA (10–5M n=6, −1±5%), or gap27 (10–4M n=11, 17±15%). With 1 stimulus, neighboring NETS arising along the same arcade arteriole are not PC (−14±1%). To test whether 2 stimuli could summate to spread RMP to a 3rd NET, we selected sequential NETS arising in alternating R – L branching patterns from an arcade (n=14). Two NETS branching R were stimulated with NP, resulting in the expected RMP of those NETS (41±6%). One NET arising L between the stimulated NETS was PC (24±8%). Two NETS arising to the L before and after the stimulated NETS were also PC (16±11%). NETS that arose sequentially next along the arcade, i.e., 2 away, were not PC (−16±6%). With dual stimulation, blocking gap junctions along the arcade between stimulated and un‐stimulated NETS, prevented spread of RMP (high OsM sucrose, 2±12%; 10–4M halothane, ‐20±1%). We conclude that an important means for amplifying a microvascular preconditioning signal is through active gap junctional activity. (NIH HL55492)