Crosstalk between the connecting tubule and the afferent arteriole regulates renal microcirculation

The renal afferent arterioles (Af-Arts) account for most of the renal vascular resistance, which is controlled similar to other arterioles and by tubuloglomerular feedback (TGF). The latter signal is generated by sensing sodium chloride concentrations in the macula densa; this in turn results in a signal which acts through the extraglomerular mesangium leading to constriction of the Af-Art. In the outer renal cortex, the connecting tubule (CNT) returns to the glomerular hilus and contacts the Af-Art suggesting that crosstalk may exist here as well. To investigate this, we simultaneously perfused a microdissected Af-Art and adherent CNT. Increasing the sodium chloride concentration perfusing the CNT significantly dilated preconstricted Af-Arts. We called this crosstalk 'connecting tubule glomerular feedback' (CTGF) to differentiate it from TGF. We tested whether entry of Na(+) and/or CI(-) into the CNT is required to induce CTGF by replacing Na(+) with choline(+). Increasing choline chloride concentration did not dilate the Af-Art. To test whether epithelial Na channels (ENaCs) mediate CTGF, we blocked ENaC with amiloride and found that the dilatation induced by CTGF was completely blocked. Inhibiting sodium chloride cotransporters with hydrochlorothiazide failed to prevent Af-Art dilatation. Finally, we tested whether nitric oxide released by the CNT mediates CTGF by the addition of a non-selective nitric oxide synthase inhibitor to the CNT. This potentiated CTGF rather than blocking it. We suggest that crosstalk exists between CNTs and attached Af-Arts, which is initiated by sodium reabsorption through amiloride-sensitive channels and this can contribute to the regulation of renal blood flow and glomerular filtration.