Derivation and validation of a machine learning risk score using biomarker and electronic patient data to predict progression of diabetic kidney disease

AIM

Predicting progression in diabetic kidney disease (DKD) is critical to improving outcomes. We sought to develop/validate a machine-learned, prognostic risk score (KidneyIntelX™) combining electronic health records (EHR) and biomarkers.

METHODS

This is an observational cohort study of patients with prevalent DKD/banked plasma from two EHR-linked biobanks. A random forest model was trained, and performance (AUC, positive and negative predictive values [PPV/NPV], and net reclassification index [NRI]) was compared with that of a clinical model and Kidney Disease: Improving Global Outcomes (KDIGO) categories for predicting a composite outcome of eGFR decline of ≥5 ml/min per year, ≥40% sustained decline, or kidney failure within 5 years.

RESULTS

In 1146 patients, the median age was 63 years, 51% were female, the baseline eGFR was 54 ml min-1 [1.73 m]-2, the urine albumin to creatinine ratio (uACR) was 6.9 mg/mmol, follow-up was 4.3 years and 21% had the composite endpoint. On cross-validation in derivation (n = 686), KidneyIntelX had an AUC of 0.77 (95% CI 0.74, 0.79). In validation (n = 460), the AUC was 0.77 (95% CI 0.76, 0.79). By comparison, the AUC for the clinical model was 0.62 (95% CI 0.61, 0.63) in derivation and 0.61 (95% CI 0.60, 0.63) in validation. Using derivation cut-offs, KidneyIntelX stratified 46%, 37% and 17% of the validation cohort into low-, intermediate- and high-risk groups for the composite kidney endpoint, respectively. The PPV for progressive decline in kidney function in the high-risk group was 61% for KidneyIntelX vs 40% for the highest risk strata by KDIGO categorisation (p < 0.001). Only 10% of those scored as low risk by KidneyIntelX experienced progression (i.e., NPV of 90%). The NRIevent for the high-risk group was 41% (p < 0.05).

CONCLUSIONS

KidneyIntelX improved prediction of kidney outcomes over KDIGO and clinical models in individuals with early stages of DKD.

Analysis of the electrophysiologic effects of short-term oxybutynin on guinea pig and rabbit ventricular cells

The objective of this study was to investigate the cardioactive properties of oxybutynin, a drug that is widely prescribed for management of voiding dysfunction. Membrane currents were recorded from whole-cell-configured guinea pig ventricular myocytes, and action potentials were recorded from guinea pig and rabbit papillary muscles. L-type Ca2+ current (I(Ca),L), inward-rectifier K+ current (I(K1)), and delayed-rectifier K+ current (I(K)) were unaffected by < or = 1 microM oxybutynin, and inhibited by higher concentrations. The concentrations that reduced the currents to one-half of predrug control amplitude (K0.5) were as follows: 1(Ca),L, 16.1 microM, I(K1), 18.2 microM, rapidly activating I(K)(I(Kr)), 11.4 microM, and slowly activating I(K)(I(Ks)), 28.7 microM. Action-potential durations at 20 and 90% repolarization (APD20, APD90) were unaffected by oxybutynin < or =3 microM in guinea pig papillary muscles driven at 1 Hz; higher concentrations selectively shortened the APD20 by as much as 25% (100 microM), and caused moderate reductions in maximal upstroke velocity. Changes in the action potentials of rabbit papillary muscles were even smaller than in the guinea pig muscles. Because the peak therapeutic plasma concentration of oxybutynin is in the 0.01-0.1 microM range, the results suggest that the drug is highly unlikely to have adverse effects on cardiac electrical activity.

Action potentials, contraction, and membrane currents in guinea pig ventricular preparations treated with the antispasmodic agent terodiline

Terodiline was widely prescribed for urinary incontinence before reports of adverse cardiac effects that included bradycardia, QT lengthening, and ventricular tachyarrhythmia. The present study on guinea pig papillary muscles and ventricular myocytes was undertaken to gain insight into the cardioactive properties of the drug. Clinically relevant concentrations (<10 microM) of terodiline lengthened the action potential duration by up to 12%; higher concentrations shortened the duration in a concentration-dependent manner. The drug depressed maximal upstroke velocity in a use-dependent manner; the IC(50) value was near 150 microM in muscles driven at 1 Hz, 60 microM at 3 Hz, 38 microM at 5 Hz, and 3 microM at 1 Hz in muscles depolarized with 14 mM K(+). Submicromolar terodiline frequently had a small positive inotropic effect, whereas micromolar concentrations depressed force in a frequency-dependent manner. Voltage-clamp results on myocytes indicate that terodiline inhibits three membrane currents that govern repolarization: 1) E4031-sensitive, rapidly activating K(+) current with an IC(50) value near 0.7 microM as previously reported; 2) slowly activating, delayed-rectifier K(+) current with an IC(50) value of 26 microM; and 3) L-type Ca(2+) current with an IC(50) value of 12 microM. These findings are correlated with the changes in action potential configuration and developed tension and discussed in relation to the cardiotoxic effects of the drug.

Block and modified gating of cardiac calcium channel currents by terodiline

1. Terodiline, an anticholinergic/antispasmodic drug effective in the treatment of urinary incontinence, is presently restricted due to adverse side effects on cardiac function. To characterize its effects on cardiac L-type Ca2+-channel current carried by Ca2+ (ICa, L) and Ba2+ (IBa,L), concentrations ranging from 0.1 to 100 microM were applied to whole-cell-configured guinea-pig ventricular myocytes. 2. Although sub-micromolar concentrations of terodiline had no effect on ICa,L at 0 mV, 100 microM drug reduced its amplitude to ca. 10% of pre-drug control. The estimated IC50 (15.2 microM in K+-dialysed cells, 12.2 microM in Cs+-dialysed cells; 0.1 Hz pulsing rate) is eight times higher than reported for ICa,L in bladder smooth muscle myocytes. 3. Terodiline affected ICa,L in a use-dependent manner; block increased when the pulsing rate was increased from 0.1 to 2 - 3 Hz, and when holding potential was lowered from -43 mV. The drug accelerated the decay of ICa,L at 0 mV in a concentration-dependent manner, and slowed the recovery of channels from inactivation. 4. Terodiline reduced peak IBa,L more effectively than peak ICa,L, and markedly accelerated the rate of inactivation of the current. 5. The results are discussed in terms of mechanisms of Ca2+ channel block and relation to the therapeutic and cardiotoxic effects of the drug.

Inhibition of cardiac inward-rectifier K+ current by terodiline

The antispasmodic agent terodiline has cardiotoxic effects that include QT lengthening. To determine whether inhibition of inwardly-rectifying K+ current (I(K1)) might be a factor in the cardiotoxicity, we measured I(K1) in guinea pig ventricular myocytes. Terodiline reduced outward I(K1) with an IC50 of 7 microM; maximal reduction was 60% with 100-300 microM concentration. Inhibition was independent of current direction, and persisted after removal of the drug. Terodiline (3-5 microM) lengthened action potentials in guinea pig papillary muscles by ca. 10%, primarily by slowing phase 3 repolarization; higher concentrations abbreviated the plateau and markedly slowed late repolarization. Terodiline washout provoked an extra lengthening, consistent with persistent inhibition of I(K1) and rapid recovery of net inward plateau current. The results suggest that inhibition of I(K1) is a likely factor in the cardiotoxicity of the drug.

Comparison of the antimuscarinic and antispasmodic actions of racemic oxybutynin and desethyloxybutynin and their enantiomers with those of racemic terodiline

Racemic oxybutynin (CAS 1508-65-2) is used clinically to treat urinary incontinence and reportedly undergoes N-deethylation to metabolites R- and/or S-desethyloxybutynin. To assess the role of these metabolites in the therapeutic effects of oxybutynin, the antimuscarinic and antispasmodic effects of RS-, R- and S-oxybutynin, RS-, R- and S-desethyloxybutynin and, for comparative purposes, RS-terodiline (CAS 7082-21-5) on isolated strips of guinea pig bladder, were examined. All of these compounds exhibited antimuscarinic activity: they competitively antagonized carbachol-induced contractions, with mean pA2 values (+/- S.E.) of 8.91 +/- 0.20, 8.80 +/- 0.27, 7.09 +/- 0.13, 8.55 +/- 0.32, 9.04 +/- 0.32, 7.31 +/- 0.35 and 6.77 +/- 0.22, respectively. Consistent with an antispasmodic action, all of the compounds produced similar inhibition of potassium-induced contraction; the mean IC50 values for reducing responses to 137.7 mmol/l potassium were between 2.22 and 5.68 mumol/l. Thus, RS- and R-oxybutynin and RS- and R-desethyloxybutynin exhibited high antimuscarinic activity relative to their antispasmodic activity, while S-oxybutynin, S-desethyloxybutynin and RS-terodiline exhibited relatively weak antimuscarinic activity. It is concluded that deethylation of oxybutynin to desethyloxybutynin does not appreciably alter its antimuscarinic or antispasmodic activity and that R- and/or S-desethyloxybutynin probably contribute significantly to the pharmacological properties of oxybutynin in humans. In addition, since the relative potency of the antimuscarinic-to-antispasmodic actions of S-oxybutynin was equivalent to that of RS-terodiline, S-oxybutynin deserves consideration for development as a single-enantiomer drug for the treatment of urinary incontinence. It may produce the same beneficial therapeutic effects as both RS-terodiline and RS-oxybutynin but, like RS-terodiline, produce a lower incidence of antimuscarinic side-effects than seen with RS-oxybutynin.

Sympathomimetic enantiomers and asthma

Airways of asthma patients can become hyperresponsive to airway spasmogens following regular use of isoprenaline or beta 2-selective sympathomimetics. Hyper-reactivity that results from acute exposure of animals to these drugs is pre-empted by vagal section (a procedure which does not influence spasmolytic efficacy of sympathomimetics), is not diminished by antagonism of beta 2-adrenoceptors and is not associated with loss of responsivity of beta 2-adrenoceptors in the airways. Since activation, modulation, or blockade of beta 2-adrenoceptors does not determine this form of hyperreactivity, the possibility that distomers may induce hyperreactivity must be considered. Ocular and vascular responses to distomers of sympathomimetics have long been recognised and, more recently, comparable observations have been made for the airways. Thus, reactivity of guinea-pig airways to spasmogens was increased following exposure to S-isoprenaline, S-salbutamol, or S-terbutaline and exposure to S-isoprenaline or S-salbutamol can intensify symptoms in asthmatics. Regular exposure to the racemate, especially during or following an allergic reaction, predisposes to expression of hyper-reactivity, which is nullified, acutely, by the eutomer. These observations imply that biological effects of sympathomimetic distomers may contribute to morbidity and mortality in asthma patients.

(S)-Albuterol increases intracellular free calcium by muscarinic receptor activation and a phospholipase C-dependent mechanism in airway smooth muscle

Racemic albuterol has been one of the most widely used beta2-adrenoceptor agonists for the relief of the symptoms of asthma, yet the use of beta2 agonists has been known to induce bronchial hyperresponsiveness. To probe a possible role of the S-enantiomer for hyperresponsiveness, we determined the effects of (S)-albuterol on intracellular Ca2+ concentration ([Ca2+]i) in dissociated bovine tracheal smooth muscle cells. Both (S)-and (R,S)-albuterol increased [Ca2+]i at concentrations of >10 pM and 1 nM, respectively, with a maximal response by 150 and 100 nM, respectively. (S)-Albuterol (1 and 10 muM) induced Ca2+ oscillations, reaching 1-2 muM [Ca2+]i. This response is in a stark contrast to that of (R)-albuterol, which decreased [Ca2+]i. The increase in [Ca2+]i was blocked by 100 nM atropine or 500 nM 4-diphenylacetoxy-N-methylpiperidine but was insensitive to the beta2 antagonist ICI 118,551 (10 muM). (S)-Albuterol (10 muM) increased inositol-1,4,5-trisphosphate levels by 213 +/- 34.4% (p < 0.05, four experiments) in cells exposed for 30 sec. The sustained phase of the Ca2+ increase was absent in Ca2+-free solution, suggesting that Ca2+ influx was responsible for the sustained Ca2+ response. The results also suggest that (S)-albuterol may cross-react with muscarinic receptors. As a Ca2+ agonist in airway smooth muscle, (S)-albuterol may have profound clinical implications because 50% of prescribed racemic albuterol is composed of (S)-albuterol.

Effects of the enantiomers of R,S-salbutamol on incompletely fused tetanic contractions of slow- and fast-twitch skeletal muscles of the guinea-pig

1. The effects of racemic R,S-salbutamol, and its individual enantiomers have been studied on incompletely fused (sub-tetanic) contractile responses of fast- and slow-contracting isolated skeletal muscles of the guinea-pig. 2. R,S-salbutamol (2-4 microM) decreased the peak force of sub-tetani in the slow-contracting soleus muscle and increased the peak force of sub-tetani in the fast-contracting peroneus longus muscle. It also increased the force of the first twitch of sub-tetani in both muscles. The decrease in the peak force of sub-tetani in the soleus muscle was due to defusion of the individual twitches caused by a shortening of their time course. 3. The effects of 4 microM of the racemate on both fast- and slow-contracting muscles were mimicked by 2 microM R-salbutamol (levalbuterol). However, 2 microM S-salbutamol was devoid of activity in both muscles. 4. We concluded that all the effects of R,S-salbutamol on guinea-pig skeletal muscles are due to the activity of the R-enantiomer. Thus there is a common enantiomeric profile for the skeletal muscle and bronchorelaxant activity of the compound.

Preclinical enantioselective pharmacology of (R)- and (S)- ketorolac

Many of the nonsteroidal anti-inflammatory drugs (NSAIDs) are marketed as racemic mixtures, composed of (R)- and (S)- enantiomers. Racemic NSAIDs are potent cyclooxygenase (COX) inhibitors only through the action of the (S)- enantiomers, as the (R)- enantiomers do not exhibit COX inhibition. However, the (R)- enantiomer of ketoprofen exhibits potent analgesic activity and minimal ulcerogenic potential. To extend these observations, we examined the (R)- and (S)- enantiomers of RS- ketorolac, (S)- ketorolac exhibited potent COX1 and COX2 enzyme inhibition, whereas (R)- ketorolac was > 100-fold less active on both COX subtypes. Both enantiomers did not affect norepinephrine or serotonin uptake sites, and nitric oxidase or lipoxygenase activities, nor did they demonstrate any affinity for opioid receptors (mu, delta, or kappa). In experimental models, (S)- ketorolac exhibited about 10-fold greater activity than (R)- ketorolac in the murine phenylquinone writhing model. In this model, morphine sulfate was effective at much lower doses, however, and neither (R)- nor (S)- ketorolac showed any morphine-sparing effect. In the rat gait test for analgesia in the foot paw after injection of brewers yeast suspension, neither (R)- nor (S)- ketorolac affected paw volume. However, both provoked changes in gait scores, the (S)- enantiomer being 30-fold more potent than the (R)- enantiomer. A similar reduction was observed with respect to ulcerogenic potential, measured by direct microscopic changes after test conclusion. These findings suggest that (R)- ketorolac may possess analgesic activity that is independent of COX inhibition and may be associated with reduced ulcerogenic potential compared to effects exhibited by (S)- ketorolac.

Enantiospecific inhibition of ligature-induced periodontitis in beagles with topical (S)-ketoprofen

Systemic and topical administration of non-steroidal anti-inflammatory drugs (NSAIDs) has been shown to reduce periodontal disease progression in both animal models and human subjects. Our present research focuses on single enantiomers of these agents to examine whether enantiospecific therapy will be efficacious in slowing periodontitis. The purpose of this study was to evaluate the inhibitory effects of (S)-ketoprofen on experimentally induced alveolar bone loss in beagle dogs. 16, 18-month-old, female beagles were brought to optimal periodontal health over a 2-week pretreatment period. Experimental periodontitis was then induced by placing silk ligatures around premolar and molar teeth and by instituting a soft, plaque-promoting diet. At baseline, animals were randomized to 1 of 4 groups, consisting of 2x daily administration of (1) placebo dentifrice, (2) 0.3% (S)-ketoprofen dentifrice, (3) 3.0% (S)-ketoprofen dentifrice, or (4) 10.0 mg (S)-ketoprofen capsules (p.o.) over a 60 day treatment period. Standardized, periapical radiographs exposed at days 1 and 60 were analyzed by computer-assisted digital radiography in order to assess the rate of alveolar bone loss. Secondary outcomes included technetium 99m-tin-diphosphonate (99mTc-Sn-MDP) uptake and the gingival index. At baseline, no differences were observed among the groups for linear bone height or 99mTc-Sn-MDP uptake ratios. From days 1 to 60, cohorts differed significantly in terms of bone loss rates (p < 0.001). In particular, beagles treated with systemic or topical (S)-ketoprofen (0.3% or 3.0% dentifrices) exhibited significantly lower mean rates of bone loss compared to placebo treated beagles (p < 0.05). Group differences in mean radiopharmaceutical uptake ratio changes approached significance (ANOVA, p = 0.07), where animals treated with topical 0.3% (S)-ketoprofen demonstrated a reduction and other groups demonstrated elevations over the 60-day dosing period. Treatment cohorts did differ significantly with respect to changes in mean gingival indices (p < 0.05). Animals treated with 0.3% or 3.0% (S)-ketoprofen dentifrice exhibited significantly reduced elevations in gingival index scores as compared to placebo treated animals. These data provide evidence that enantiospecific therapy with (S)-ketoprofen, topically or systemically delivered, may alter the progression of periodontal disease in the beagle dog model.

Cardioprotective profile of the cardiac-selective ATP-sensitive potassium channel opener BMS-180448

ATP-sensitive potassium channel (KATP) openers have direct protective effects on ischemic myocardium that are independent of vasorelaxation. Because reference KATP openers (e.g., cromakalim, pinacidil) are potent relaxants of smooth muscle, their utility for treating myocardial ischemia may be limited by hypotension. Efforts aimed at development of a cardioprotective KATP opener with less vasorelaxant activity led to identification of the arylcyanoguanidine analogue BMS-180448. In globally ischemic rat hearts, BMS-180448 was cardioprotective (EC25 for increasing time to contracture = 2.5 microM), with potency equal to that of cromakalim (EC25 = 4.9 microM) despite being significantly less potent as a peripheral smooth muscle relaxant (methoxamine-constricted rat aorta). The cardioprotective effects of BMS-180448 in isolated perfused rat heart were abolished by the KATP blockers glyburide and sodium 5-hydroxydecanoate, indicating KATP involvement in its mechanism of action. Further confirmation was obtained by demonstration of single KATP opening by BMS-180448 in guinea pig cardiac myocytes. In anesthetized dogs, cromakalim was > 100-fold more potent than BMS-180448 in decreasing blood pressure (BP). In anesthetized dogs subjected to 90-min coronary occlusion/reperfusion, BMS-180448 reduced infarct size (IS) by 50% without hemodynamic effects. BMS-180448 provides the opportunity to explore the cardioprotective actions of this class of agents without the possible complications (hypotension, coronary steal) that may be caused by the currently available KATP openers.

Effects of cromakalim or pinacidil on pacing- and ischemia-induced ventricular fibrillation in the anesthetized pig

The effects of the potassium channel openers (KCO), cromakalim or pinacidil, were evaluated in an anesthetized porcine model of pacing- and ischemia-induced ventricular fibrillation (VF). Hearts were paced at 180 bpm and the left anterior descending coronary artery was occluded until VF was induced. Reproducible times to VF (in seconds) were obtained allowing at least 20 min recovery following defibrillation. Cromakalim (0.3 mg/kg) or pinacidil (3 mg/kg) produced equivalent drops in mean arterial blood pressure. At these doses, cromakalim reduced monophasic action potential duration measured at 90% repolarization (APD90). Although time to VF in the cromakalim group was significantly greater than the vehicle treated group, it was not significantly different from its predrug value. In contrast, pinacidil reduced APD90, and significantly increased time to VF from 134 +/- 5 to 322 +/- 62 s (p < 0.05). Neither cromakalim nor pinacidil affected whole-cell calcium currents recorded in guinea pig myocytes. During ischemia, cromakalim or pinacidil further reduced APD90; however, pinacidil had a two-fold greater effect than did cromakalim. The Class III antiarrhythmic agent, dofetilide, prolonged APD90, but did not increase time to VF. In conclusion, the increased time to VF observed with pinacidil coincides with its ability to shorten APD, and is consistent with activation of ATP-sensitive K+ channels (K+ ATP). It is suggested that indirect reduction of calcium influx through K+ ATP activation and APD shortening is sufficient to increase time to VF in this model. However, the inability of dofetilide to be effective suggests that this model would not be useful to test for Class III antiarrhythmic agents.

Cardioprotective effects of a novel calcium antagonist related to the structure of cromakalim

A novel pyranoquinoline analog (BMS-188107) of the ATP-sensitive potassium channel (KATP) opener cromakalim was previously shown to be devoid of KATP opening activity in nonischemic myocardium and vascular smooth muscle, but appeared to be a relatively potent calcium antagonist. This clear differentiation between channels within a structural series is a novel finding. With the idea that KATP openers are often more active in ischemic relative to nonischemic myocardium, we determined the cardioprotective effects of this agent in isolated rat hearts and whether these anti-ischemic effects are abolished by KATP blockade. Isolated rat hearts were subjected to 25 min of global ischemia and 30 min of reperfusion and the severity of ischemic/reperfusion injury was determined. BMS-188107 was given before ischemia at 0.5 to 10 microM. Pretreatment (before ischemia) with BMS-188107 caused significant cardiodepressant activity and increased coronary flow only at a concentration of 10 microM, although modest negative inotropic effects were observed at the 0.5 and 1 microM concentrations. Significant improvements in postischemic contractile function and reductions in lactate dehydrogenase release were observed with 1 to 10 microM BMS-188107, indicating significant reductions in ischemic/reperfusion injury. Neither the pre- nor the postischemic effects of 1 to 10 microM BMS-188107 were significantly altered by the KATP blockers sodium 5-hydroxydecanoate (100 microM) or glyburide (1 microM). Previous studies did not determine the effect of BMS-188107 on sodium channels and thus, the effect of this agent on maximum upstroke velocity of the action potential was determined.(ABSTRACT TRUNCATED AT 250 WORDS)

The cardioprotective, vasorelaxant and electrophysiological profile of the large conductance calcium-activated potassium channel opener NS-004

A series of compounds have been reported which open the large conductance calcium activated potassium channel (maxi-K). By utilizing the most potent compound, NS-004 [1-(5-chloro-2-hydroxyphenyl)-5-trifluromethyl-1,3-dihydro-2-be nzimidazol-2- one], we studied the role of maxi-K channels in ischemic myocardium. Isolated rat hearts were pretreated with vehicle or NS-004 (6-36 microM). NS-004 caused a concentration-dependent reduction in left ventricular developed pressure and an increase in coronary flow. In global ischemia (25 min), a concentration-dependent increase in time to contracture was found in NS-004 (6-20 microM)-treated hearts (EC25 = 8.6 microM). Neither iberiotoxin (50 nM), a maxi-K blocker, nor glyburide (1 microM), an adenosine triphosphate-sensitive potassium channel blocker, reversed the preischemic or ischemic effects of 20 microM NS-004. NS-004 relaxed phenylephrine- and KCl- contracted rat aortic smooth muscle (IC50 = 9.2 microM). This relaxation was unaffected by 50 and 200 nM iberiotoxin. Whole cell potassium currents in ventricular myocytes demonstrated no significant increases in outward potassium current after treatment with NS-004 (1-20 microM). A small, but significant, increase in outward potassium current was observed with 50 microM NS-004. When peak inward L-type calcium currents were measured in ventricular myocytes, a concentration-dependent inhibition was observed in the presence of NS-004 (1-50 microM). Iberiotoxin (50 nM) did not alter the inhibition of inward calcium current observed in the presence of NS-004.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of rabbit aortic Ca(2+)-activated K+ channels by pinacidil, cromakalim, and glibenclamide

Rabbit aortic smooth muscle microsomes were isolated and large-conductance Ca(2+)-activated K+ (BK) channels incorporated into planar lipid bilayers. The selectivity sequence and relative permeability ratios for monovalent cations was K+ (1.0) > Rb+ (0.68) > NH4+ (0.14) >> Na+, Cs+ (< 0.05). Application of pinacidil or cromakalim (0.05-10 microM) shifted the probability of opening (Po)-voltage relationship in the hyperpolarizing direction. The concentrations of pinacidil and cromakalim required to increase Po 50% of the maximum value at -40 mV were 0.96 +/- 0.04 and 0.52 +/- 0.03 microM, respectively. Neither pinacidil nor cromakalim altered the voltage sensitivity of the channel (11-13 mV/e-fold change in Po). Kinetic analysis of data at -40 mV demonstrated that pinacidil (1 microM) decreased the length of time the channel dwelled in its long-closed state by 50% from 173 +/- 50 to 86 +/- 19 ms. No significant change was observed for the open time constant (20 ms). Glibenclamide (10 microM) had no effect on Po of BK channels. However, glibenclamide reversed the pinacidil- or cromakalim-stimulated increase in Po of BK channels. These data suggest that both cromakalim and pinacidil increased the probability of opening of single rabbit aortic large-conductance Ca(2+)-activated K+ channels and that this channel modulation may contribute to the vasorelaxant properties of these drugs.

Effect of the phospholipase A2 inhibitors quinacrine and 7,7-dimethyleicosadienoic acid in isolated globally ischemic rat hearts

Phospholipase A2 (PLA2) activity results in the formation of lysophospholipids and free fatty acids which may contribute to ischemic myocardial dysfunction. We evaluated the cardioprotective activity of two putative PLA2 inhibitors, quinacrine and 7,7-dimethyleicosadienoic acid (DEDA), in isolated globally ischemic rat hearts. Pretreatment with 1, 5 and 50 microM quinacrine before ischemia did not alter coronary flow but did cause significant cardiodepression. Twenty five minutes of global ischemia and 30 min of reperfusion caused severe myocardial dysfunction and lactate dehydrogenase release. Quinacrine significantly improved reperfusion contractile function and reduced lactate dehydrogenase release, indicative of cardioprotection. In contrast, 30 to 100 microM DEDA produced neither preischemic cardiodepression nor cardioprotective activity. PLA2 inhibition was inferred from measurements of the prostacyclin metabolite, 6-keto-prostaglandin F1 alpha in the coronary effluent and myocardial palmitoyl-lysophosphatidylcholine. Quinacrine and DEDA reduced both 6-keto-prostaglandin F1 alpha and palmitoyl-lysophosphatidylcholine by similar degrees. These results suggest that the cardioprotective activity of quinacrine is independent of PLA2 inhibition. A possible role of calcium inhibition was investigated in rat aortic smooth muscle strips. Norepinephrine-, KCl- and BAY K8644-induced contractions were antagonized in the presence of 5 and 50 microM quinacrine, but were unaffected by 30 to 60 microM DEDA. The ability of quinacrine to inhibit calcium was investigated further in cardiac ventricular myocytes. Measurement of mean whole cell calcium currents showed that quinacrine (5 microM) could inhibit this current up to 70%. Thus, these results suggest that quinacrine-induced cardioprotection may not be due to PLA2 inhibition, but may be related to calcium entry blocking activity.

Specific block of the anti-ischemic actions of cromakalim by sodium 5-hydroxydecanoate

The potassium channel activators cromakalim and pinacidil were recently shown to have anti-ischemic properties in isolated globally ischemic rat hearts. The effects of two reported blockers of ATP-sensitive potassium channels, glibenclamide (glyburide) and sodium 5-hydroxydecanoate, on the anti-ischemic efficacy of cromakalim were determined in this model. Buffer-perfused rat hearts were subjected to 25 minutes of ischemia followed by 30 minutes of reperfusion. Pretreatment of these hearts with 60 microM cromakalim significantly decreased indexes of contractile function but caused a significant improvement of postreperfusion function and a significant decrease in release of lactate dehydroxygenase and in end-diastolic pressure. Pretreatment with glibenclamide at concentrations that reversed the preischemic effects of cromakalim (0.05 and 1.0 microM) also significantly reversed its postischemic protective effects. Sodium 5-hydroxydecanoate (100 and 300 microM) had no effect on the preischemic (negative inotropic) effects of cromakalim but completely reversed its cardioprotective effects. Sodium 5-hydroxydecanoate did not reverse the cardioprotective effects of the calcium entry blocker diltiazem. In phenylephrine-contracted rat aorta, glibenclamide (0.1-10 microM) inhibited cromakalim-induced relaxation, whereas sodium 5-hydroxydecanoate (10-1,000 microM) had no effect. Similarly, the ability of cromakalim to shorten cardiac action potential duration in guinea pig papillary muscle and to increase outward whole-cell potassium currents in isolated myocytes was inhibited by glibenclamide, whereas sodium 5-hydroxydecanoate was without effect. Thus, both glibenclamide and sodium 5-hydroxydecanoate inhibited the effects of cromakalim after reperfusion; however, sodium 5-hydroxydecanoate, unlike glibenclamide, had no effect in nonischemic preparations. These results suggest that sodium 5-hydroxydecanoate is an ischemia-selective inhibitor of ATP-sensitive potassium channels.

Structurally novel antihypertensive compound, McN-5691, is a calcium channel blocker in vascular smooth muscle

These studies were conducted to gain greater understanding of the mechanism of action of the chemically novel antihypertensive agent, McN-5691. McN-5691 (1 and 10 microM) prevented 60 mM KCl-induced contraction and calcium uptake and caused concentration-dependent relaxation (EC50 = 190 microM) of 30 mM KCl-contracted aortic rings. At or below 10 microM, McN-5691 had no effects on basal tone or calcium uptake (45Ca) in isolated rings of rabbit thoracic aorta. McN-5691 caused complete high affinity inhibition (Kd = 39.5 nM) of specific diltiazem binding to the benzothiazepine receptor on the voltage-sensitive calcium channel in skeletal muscle microsomal membranes. In contrast to diltiazem, McN-5691 inhibited specific dihydropyridine receptor binding, but the effect was biphasic with high (Kd = 4.7 nM) and low (Kd = 919.8 nM) affinity components. These findings suggest that McN-5691 is a voltage-sensitive calcium channel blocker. Unlike other calcium channel blockers, McN-5691 inhibited norepinephrine (NE)-induced contraction (10 microM) and calcium uptake (1 and 10 microM) and caused concentration-dependent relaxation (EC50 = 159 microM) of 1 microM NE-contracted rings of rabbit thoracic aorta. The vascular relaxant effects of McN-5691 were not related to increased calcium (45Ca) efflux from vascular smooth muscle cells. The effects of McN-5691 on NE-induced contraction were unrelated to intracellular mechanisms because McN-5691 did not affect NE-induced contraction in the absence of extracellular calcium. McN-5691 had weak activity in rat cerebral cortical membrane alpha-1 or alpha-2 adrenergic receptor binding assays. McN-5691-induced vasodilation of phenylephrine-contracted rat aortic strips was not reversible by high potassium, indicating that McN-5691 does not induce relaxation of blood vessels through potassium channel activation. In summary, these studies suggest that the primary vasodilator mechanism of McN-5691 is calcium channel blockade through competitive binding at the diltiazem site on the voltage sensitive calcium channel. McN-5691 may possess an additional vasodilator mechanism of action distinct from alpha adrenergic receptor blockade but involving a cell membrane-related event apparently leading to attenuation of receptor-operated calcium channel activity.

Two stable levels of diastolic potential at physiological K+ concentrations in human ventricular myocardial cells

Cells in many specimens of human ventricle can exhibit either of two stable levels of diastolic potential (DP) when exposed to 4 mM K+ in vitro (i.e., -78 +/- 4 mV or -45 +/- 5 mV, mean +/- SEM). In this report we show that the DP of some partially depolarized human ventricular cells developed a sustained 25-35 mV hyperpolarization (n = 28) when bath K+ concentration (K+b) was raised from 4 to 7 mM. On return of K+b to 4 mM, the DP of most, but not all, of these cells returned to the original depolarized levels. In other cells, the transition between the two levels of DP occurred at variable K+b ranging from 1 to 20 mM. We investigated the ionic mechanism(s) underlying the shifts between the two levels of potential by studying the K+ dependence of the DP in partially depolarized cells in 22 specimens of human ventricle. DP hyperpolarized an average of 25.6 mV (from -44.4 +/- 1.3 to -70.0 +/- 1.3 mV; n = 25) when K+b was increased from 4 to 7 mM. Intracellular K+ activity, determined by K+-selective microelectrodes, was within the range of normal reported for other mammalian species (106.7 +/- 4.4 mM in 4 mM K+; n = 22) and was unaffected by increasing K+b to 7 mM (111.7 +/- 6.6 mM; n = 6). Ba2+ (0.05 mM), a blocker of the inward rectifying K+ current, reversibly prevented the hyperpolarization, whereas acetylstrophanthidin (9 microM) failed to inhibit it. These results suggest that the hyperpolarization was due to a K+-dependent increase in K+ permeability and that electrogenic sodium pumping did not contribute significantly to the process. The ionic basis of the depolarization from a hyperpolarized level of DP also was investigated. Decreasing bath Na+ concentration and exposure to 30 microM tetrodotoxin did not prevent the depolarization. However, the depolarization could be inhibited by 2 mM Mn2+. These findings suggest that the depolarization may have been due to a Mn2+-sensitive inward current.

Anti-ischemic effects of the potassium channel activators pinacidil and cromakalim and the reversal of these effects with the potassium channel blocker glyburide

The direct cardioprotective efficacy of the potassium channel activators pinacidil and cromakalim was determined in isolated globally ischemic rat hearts. Isolated buffer-perfused rat hearts were subjected to 25 min of ischemia followed by 30 min of reperfusion. These hearts were pretreated with 1 to 100 microM pinacidil, 1 to 7 microM cromakalim or vehicle. Pinacidil resulted in significant improvements in reperfusion function and cardiac compliance, though it did not significantly reduce lactate dehydrogenase release at any concentration. The protective effects of pinacidil were greatest at a 10 microns concentration and were slightly diminished at higher concentrations (30 and 100 microns). Although not affecting the severity of ischemia alone, 10 microM glyburide (potassium channel blocker) completely reversed the protective effects of pinacidil on reperfusion function and compliance. Cromakalim (7 microM) resulted in a greater than 50% improvement in reperfusion function and compliance and unlike pinacidil significantly reduced lactate dehydrogenase release by approximately 50%. At 1 microM, glyburide alone did not significantly affect the severity of ischemia but reversed the protective effects of cromakalim. Not only did glyburide reverse the protective effects of cromakalim, it resulted in a worsening of ischemia compared to vehicle, an effect not seen with glyburide alone. Thus, both pinacidil and cromakalim appear to have direct cardioprotective efficacy, though some differences between them may be possible. The mechanism of their protective effects appears to be via potassium channel opening as the potassium channel blocker glyburide reverses the protective effect of these compounds. Intracellular electrophysiological studies showed that ischemia-induced depolarization was reversed with cromakalim, which increased the resting potential nearly back to preischemic levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Intra- and extracellular potassium activities and the potassium equilibrium potential in partially depolarized human atrial cells

Under tissue bath conditions, isolated specimens of human right atrium are characterized by the presence of large numbers of partially depolarized cells. The basis for the depolarization is still not understood. To determine if reduced intracellular potassium activity (aKi) is responsible for the low levels of maximum diastolic potential (MDP), aKi was directly measured with potassium ion-selective micro-electrodes (KISE). The effects of varying bath potassium concentration ([K+]0) on aiK and on the relationship between MDP and the potassium equilibrium potential (EK) also were determined. In 4 mM [K+]0, all specimens studied were partially depolarized (MDP = -43.9 +/- 1.3 mV [mean +/- S.E.]) and beat spontaneously. aKi was 98.1 +/- 1.5 mM, and EK was -93.3 +/- 0.4 mV. Changes in [K+]0 between 2.5 and 40 mM did not change aKi significantly. MDP was relatively insensitive to [K+]0 and was always far positive to EK over the entire range of [K+]0 studied. The ability of the KISE to reliably measure aKi in the face of the spontaneous diastolic depolarization was assessed by using acetylcholine or cooling to depress automaticity. These measures did not significantly alter the calculated aKi. The results indicate that: aKi in human atrial specimens is similar to that in atria from other mammalian species, and the low level of MDP exhibited by human atrial cells subject to conventional tissue bath conditions does not primarily result from low levels of aKi.

Modulation of auditory evoked magnetic fields by benzodiazepines

The N1 and P2 components of the auditory evoked magnetic field were shown to be modified by the benzodiazepines diazepam and triazolam. Previous studies indicate that the electrical sources of these components are located in the auditory cortex, implying that benzodiazepines have a direct or indirect effect on neuronal activity at this level. The recorded changes were comparable to those previously reported using auditory evoked potential measurements. These results suggest that magnetic recordings may eventually be used as a sensitive, supplementary and location-specific measure of the central action of psychoactive substances.

Evidence for electrogenic Na+ pumping in human atrial myocardium

The resting potential of "sodium-loaded' cardiac cells can transiently hyperpolarize to levels negative to the steady state resting potential [3,5,6]. Hyperpolarization is associated with the coupled efflux of Na+ and influx of K+ driven by an active transport process and may result from an increased K+ equilibrium potential (EK), an outward pump current or both. Using conventional microelectrode techniques, we found that Na+-loaded human atrial myocardium can also transiently hyperpolarize. Na+ loading was induced by cooling to 2 degrees to 3 degrees C. Upon rewarming to 37 degrees C in a 20 mM K+ solution, the resting potential transiently hyperpolarized to levels at least 11 mV negative to the calculated EK and 29 +/- 2 mV (mean +/- S.E.) negative to the steady state level (- 33 +/- 2 mV) recorded some 15-20 minutes later. An increase in K+ conductance induced by acetylcholine exposure [2,7,10] during the transient hyperpolarization caused a depolarization, indicating that the resting potential was indeed negative to EK. These findings cannot be explained by either conductance changes or electroneutral Na+ pumping and concomitant extracellular K+ depletion. We conclude that the Na+-loaded human atrium can generate net pump current.

Directional pedestal-free laser Doppler velocimetry without frequency biasing. Part 1

The spatial structure of the optical field on the detector of a laser Doppler velocimeter is examined. It is shown that for sufficiently small scatterers, the optical field is a traveling wave of shape determined by the detector optics alone. The direction of travel of the optical field reflects that of the scattering particle. Thus, the direction of motion of the particle is determined by temporal correlation of photocurrents from two spatially offset detector arrays. The arrays also eliminate the Doppler pedestal as shown by Ogiwara (1979). In this paper, the theory of the new method is described; experimental implementation will be described in a complementary paper.

Ionic currents in the uterine smooth muscle

1. Short segments of isolated longitudinal myometrium from the pregnant rate uterus have been studied in a double sucrose-gap voltage-clamp arrangement. The clamped segment averaged 65 mum times 240 mum times 100 mum, has an average total capacitance of 0-14 muF, and may contain 50-200 individual myometrial cells. 2. A significant resistance exists in series with the membrane, and limits theprecision of the quantitative information. However, it is argued that some qualitative and some comparative information is useful. 3. In Krebs-bicarbonate solution, depolarizing steps produced initial transient inward currents followed by delayed outward currents. 4. When [Na+]o was reduced by 50%, the equilibrium potential Ea shifted by an average of -17-6 mV, the maximum inward current was reduced to 0-5, the time to peak of the early current was delayed by 1-1 msec, and the maximum chord conductances for the early(Ga) and late (GK) currents remained unchanged as compared with those in normal [Na+]o. 5. When [Ca2+] was reduced to 25% of normal, Ea shifted by an average of -20-3 mV, the maximum inward current was reduced to 0-5, the time to peak was delayed 3-1 msec, and Ga was significantly reduced, while GK was unaffected. 6. The early current, and its tail when repolarization was imposed, reversed direction from inward to outward when [Na+]o was reduced from 143 mM to zero, with [Ca2+]o remaining constant at 1-9 mM. 7. From the observations in 4, 5 and 6, it was concluded that Na+ is the main charge carrier for the early current, and that Ca2+ is important in regulating Ga. 8. The late current is outwards when [K+]o equals 5-9 mM, but inwards in some voltage range when [K+]o was elevated to 120 or 148 mM. K+ is the main charge carrier for the late current. 9. The equilibrium potential for the late current, EK, is about 15 mV more negative than the natural resting potential. 10. Prolonged holding of the preparations at voltages that differ significantly from the natural resting potential tends to shift EK in a way consistent with passive changes in [K+]i by the holding current. 11. The steady-state inactivation of the early current, h, is unusual. Inward current is macimum around the resting potential, and declines with both hyperpolarizing and depolarizing changes. Half-inactivation occurred with about 9 mV depolarization and 15 mV hyperpolarization. 12. The instantaneous current-voltage relations of both early and late currents are linear. The chord conductances Ga and GKare similar in form to those in other tissues.