Diabetes and hypertension are the leading causes of chronic kidney disease and their incidence is increasing at an alarming rate. Both are associated with impairments in the autoregulation of renal blood flow (RBF) and greater transmission of fluctuations in arterial pressure to the glomerular capillaries. The ability of the kidney to maintain relatively constant blood flow, glomerular filtration rate (GFR) and glomerular capillary pressure is mediated by the myogenic response of afferent arterioles working in concert with tubuloglomerular feedback that adjusts the tone of the afferent arteriole in response to changes in the delivery of sodium chloride to the macula densa. Despite intensive investigation, the factors initiating the myogenic response and the signaling pathways involved in the myogenic response and tubuloglomerular feedback remain uncertain. This review focuses on current thought regarding the molecular mechanisms underlying myogenic control of renal vascular tone, the interrelationships between the myogenic response and tubuloglomerular feedback, the evidence that alterations in autoregulation of RBF contributes to hypertension and diabetes-induced nephropathy and the identification of vascular therapeutic targets for improved renoprotection in hypertensive and diabetic patients.

Restorative/protective therapies to restore dopamine neurons in the substantia nigra pars compacta (SNpc) are greatly needed to effectively change the debilitating course of Parkinson's disease. In this study, we tested the therapeutic potential of a neurogenic neurosteroid, allopregnanolone, in the restoration of the components of the nigrostriatal pathway in MPTP-lesioned mice by measuring striatal dopamine levels, total and tyrosine hydroxylase immunoreactive neuron numbers and BrdU-positive cells in the SNpc. An acute treatment (once/week for two weeks) with allopregnanolone restored the number of tyrosine hydroxylase-positive and total cell numbers in the SNpc of MPTP-lesioned mice, even though this did not increase striatal dopamine. It was also noted that MPTP treated mice to which allopregnanolone was administered had an increase in BrdU-positive cells in the SNpc. The effects of allopregnanolone in MPTP-lesioned mice were more apparent in mice that underwent behavioral tests. Interestingly, mice treated with allopregnanolone after MPTP lesion were able to perform at levels similar to that of non-lesioned control mice in a rotarod test. These data demonstrate that allopregnanolone promotes the restoration of tyrosine hydroxylase immunoreactive neurons and total cells in the nigrostriatal tract, improves the motor performance in MPTP-treated mice, and may serve as a therapeutic strategy for Parkinson's disease.

Recent studies suggest that certain acid-sensing ion channels (ASIC) are expressed in vascular smooth muscle cells (VSMCs) and are required for VSMC functions. However, electrophysiological evidence of ASIC channels in VSMCs is lacking. The purpose of this study was to test the hypothesis that isolated cerebral artery VSMCs express ASIC-like channels. To address this hypothesis, we used RT-PCR, Western blotting, immunolabeling, and conventional whole cell patch-clamp technique. We found extracellular H+-induced inward currents in 46% of cells tested ( n = 58 of 126 VSMCs, pH 6.5–5.0). The percentage of responsive cells and the current amplitude increased as the external H+ concentration increased (pH6.0, n = 28/65 VSMCs responsive, mean current density = 8.1 ± 1.2 pA/pF). Extracellular acidosis (pH6.0) shifted the whole cell reversal potential toward the Nernst potential of Na+ ( n = 6) and substitution of extracellular Na+ by N-methyl-d-glucamine abolished the inward current ( n = 6), indicating that Na+ is a major charge carrier. The broad-spectrum ASIC blocker amiloride (20 μM) inhibited proton-induced currents to 16.5 ± 8.7% of control ( n = 6, pH6.0). Psalmotoxin 1 (PcTx1), an ASIC1a inhibitor and ASIC1b activator, had mixed effects: PcTx1 either 1) abolished H+-induced currents (11% of VSMCs, 5/45), 2) enhanced or promoted activation of H+-induced currents (76%, 34/45), or 3) failed to promote H+ activation in nonresponsive VSMCs (13%, 6/45). These findings suggest that freshly dissociated cerebral artery VSMCs express ASIC-like channels, which are predominantly formed by ASIC1b.

Mean concentrations of ANID and CASP were associated with statistically significant decreases in left ventricular contractility at concentrations that may be achievable in humans after peripheral administration, while MICA caused no change. TEM studies suggest this may be a result of mitochondrial damage. Caution may be warranted with central administration of these agents to patients with preexisting cardiac dysfunction.

The effects of the n-alkyl derivatives of guanidine on the frog neuromuscular junction were studied using the two-microelectrode voltage clamp and other eleetrophysiological techniques. Methyl-, ethyl-, and propylguanidine stimulated the nerve-evoked release of transmitter. However, amyland octylguanidine had no apparent presynaptic action. All of the derivatives blocked the postsynaptic response to acetylcholine, the potency sequence being octyl-> amyl-> propyl-, methyl-> ethylguanidine. Methyl-and octylguanidine did not protect the receptor from a-bungarotoxin block, suggesting that these compounds do not bind to the receptor but probably block the ionic channel. Methyl-, ethyl-, and propylguanidine shortened inward endplate currents but prolonged outward currents. Amylguanidine prolonged both inward and outward endplate currents, and the currents became biphasic at negative membrane potentials. Octylguanidine increased the rate of decay of endplate currents at all potentials. All of the derivatives blocked inward endplate currents more markedly than outward currents, resulting in a highly nonlinear current-voltage relation. Methyl-, ethyl-, and propylguanidine reversed the voltage dependence of endplate current decay, while amyl-and octylguanidine reduced the voltage dependence of endplate current decay. Octylguanidine appears to block the ionic channel in both the open and the closed state. The block of the open channel follows pseudo-first-order kinetics with a forward rate constant of 4-6 • 107 M -1 s-1.

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A BST RA CT The effects of n-alkylguanidine derivatives on sodium channel conductance were measured in voltage clamped, internally perfused squid giant axons. After destruction of the sodium inactivation mechanism by internal pronase treatment, internal application of n-amylguanidine (0.5 mM) or noctylguanidine (0.03 raM) caused a time-dependent block of sodium channels. No time-dependent block was observed with shorter chain derivatives. No change in the rising phase of sodium current was seen and the block of steadystate sodium current was independent of the membrane potential. In axons with intact sodium inactivation, an apparent facilitation of inactivation was observed after application of either n-amylguanidine or n-octylguanidine. These results can be explained by a model in which alkylguanidines enter and occlude open sodium channels from inside the membrane with voltage-independent rate constants. Alkylguanidine block bears a close resemblance to natural sodium inactivation. This might be explained by the fact that alkylguanidines are related to arginine, which has a guanidino group and is thought to be an essential amino acid in the molecular mechanism of sodium inactivation. A strong correlation between alkyl chain length and blocking potency was found, suggesting that a hydrophobic binding site exists near the inner mouth of the sodium channel.

The acetylcholine-(ACh-)activated channels of chick myotubes were studied by the patch-clamp method. Single-channel amplitudes were measured over a wide range of potentials in solutions of cesium, arginine, and three small amines. Symmetrical, isotonic cesium solutions gave a linear I-V relationship with the single-channel conductance, gamma, of 42 pS at 11 degrees C. Dilutions of cesium by mannitol shifted the reversal potential 23.9 mV per e-fold change in internal cesium concentration. Selectivity, as defined by reversal potential criteria, depended on the molecular size of the permeant cation. The Q10 of gamma for the symmetrical isotonic cesium solutions as well as internal isotonic methylamine was 1.3-1.4. These properties are qualitatively similar to those seen at the ACh-activated channel of the frog neuromuscular junction. Partially substituting arginine for internal cesium depressed outward currents. 80 mM arginine acted equally well from the inside or the outside, as if arginine transiently blocks the ACh-activated channel in a current dependent way. Diluting internal cesium almost 10-fold, from 320 to 40 mM, increased the permeability of the channel calculated from Goldman-Hodgkin-Katz equations by almost threefold. Thus, cesium itself appears to block with a dissociation constant of 135 mM. Methylamine blocked the channel approximately as well as did cesium. Ammonia and ethylamine blocked the channel somewhat more than cesium. We conclude that (a) the channel is qualitatively similar to that of frog neuromuscular junction, (b) cations bind within the channel, and (c) arginine decreases channel conductance equally whether applied from the inside or the outside.