Myogenic and Ca 2+ spark mediated mechanisms of vascular diameter control differ between genders and between the spiral modiolar artery and radiating arterioles

Blood flow regulation is critical for hearing due to the exquisite sensitivity of the cochlea to ischemia and oxidative stress. Similar to the brain, the cochlea can autoregulate flow within normal limits despite variations of systemic blood pressure. The site of autoregulation along the vascular tree, myogenic control of vascular diameter and the role of Ca 2+ sparks remained undetermined. In this study, spiral modiolar arteries (SMA) and radiating arterioles (RA) from male and female gerbils were isolated and pressurized using concentric pipette systems. Inner diameter (ID) and Ca 2+ sparks, visualized by fluo4, were recorded by confocal laser scanning microscopy. Percent myogenic tone was calculated as (ID passive − ID active ) × 100/ID passive , with ID passive detected in Ca 2+ ‐free solutions and ID active detected in the presence of 1 mM Ca 2+ and 10 μM L‐NNA. At 60 cmH 2 O, which is close to estimated pressure in vivo, ID passive was gender‐independent; SMA: 78.3±2.6 μm (n=13) and RA: 51.2±1.7 μm (n=8). Myogenic tone was different in male SMA (~15% at ≥30 cmH 2 O) compared to female SMA (~5% at ≥60 cmH 2 O) whereas myogenic tone in RA was gender‐independent (~15% at ≥60 cmH 2 O). Ca 2+ sparks at 60 cmH 2 O in female SMA and RA were similar in frequency (0.89±0.07 Hz, n=17 vs 0.91±0.09 Hz, n=37), and in sensitivity to 10 μM ryanodine. Increases in pressure increased spark frequency at individual sites in SMA but not in RA. Recruitment of additional spark sites was observed in RA but not in SMA. In conclusion, myogenic and Ca 2+ spark mediated mechanisms of vascular diameter control differed between genders and different segments of the cochlear vasculature. Supported by NIH‐R01‐DC04280 and NIH‐P20‐RR017686.