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Despite the important roles played by ventricular fibroblasts and myofibroblasts in the formation and maintenance of the extracellular matrix, neither the ionic basis for membrane potential nor the effect of modulating membrane potential on function has been analyzed in detail. In this study, whole cell patch-clamp experiments were done using ventricular fibroblasts and myofibroblasts. Time- and voltage-dependent outward [K.sup.+] currents were recorded at depolarized potentials, and an inwardly rectifying [K.sup.+] (Kir) current was recorded near the resting membrane potential (RMP) and at more hyperpolarized potentials. The apparent reversal potential of Kir currents shifted to more positive potentials as the external [K.sup.+] concentration ([[K.sup.+]]o) was raised, and this Kir current was blocked by 100-300 [micro]M B[a.sup.2+]. RT-PCR measurements showed that mRNA for Kir2.1 was expressed. Accordingly, we conclude that Kir current is a primary determinant of RMP in both fibroblasts and myofibroblasts. Changes in [[K.sup.+]]o influenced fibroblast membrane potential as well as proliferation and contractile functions. Recordings made with a voltage-sensitive dye, DiBA[C.sub.3](4), showed that 1.5 mM [[K.sup.+]]o resulted in a hyperpolarization, whereas 20 mM [[K.sup.+]]o produced a depolarization. Low [[K.sup.+]]o (1.5 mM) enhanced myofibroblast number relative to control (5.4 mM [[K.sup.+]]o). In contrast, 20 mM [[K.sup.+]]o resulted in a significant reduction in myofibroblast number. In separate assays, 20 mM [[K.sup.+]]o significantly enhanced contraction of collagen I gels seeded with myofibroblasts compared with control mechanical activity in 5.4 mM [[K.sup.+]]o. In combination, these results show that ventricular fibroblasts and myofibroblasts express a variety of [K.sup.+] channel [alpha]-subunits and demonstrate that Kir current can modulate RMP and alter essential physiological functions. rat ventricle; voltage clamp

An imaging system suitable for recordings from Langendorff-perfused rat hearts using the voltage-sensitive dye 4-[beta]-[2-(di-n-butylamino)-6-naphthyl]vinyl]pyridinium (di-4-ANEPPS) has been developed. Conduction velocity was measured under hyper- and hypokalemic conditions, as well as at physiological and reduced temperature. Elevation of extracellular [[K.sup.+]] to 9 mM from 5.9 mM caused a slowing of conduction velocity from 0.66 [+ or -] 0.08 to 0.43 [+ or -] 0.07 mm/ms (35%), and reduction of the temperature to 32[degrees]C from 37[degrees]C caused a slowing from 0.64 [+ or -] 0.07 to 0.46 [+ or -] 0.05 mm/ms (28%). Ventricular activation patterns in sinus rhythm showed areas of early activation (breakthrough) in both the right and left ventricle, with breakthrough at a site near the apex of the right ventricle usually occurring first. The effects of mechanically immobilizing the preparation to reduce motion artifact were also characterized. Activation patterns in epicardially paced rhythm were insensitive to this procedure over the range of applied force tested. In sinus rhythm, however, a relatively large immobilizing force caused prolonged PQ intervals as well as altered ventricular activation patterns. The time-dependent effects of the dye on the rat heart were characterized and include 1) a transient vasodilation at the onset of dye perfusion and 2) a long-lasting prolongation of the PQ interval of the electrocardiogram, frequently resulting in brief episodes of atrioventricular block. fluorescent dyes; rat heart ventricular activation; imaging techniques

Aluminum toxicity often reduces plant growth on acid soils, and coal combustion by-product (CCBPs) can partially mitigate acid soil effects. Columns containing acidic (pH 4.7) Lily soil (Typic Hapludult) were amended in the upper 15 cm with CCBPs, lime, or both. Amendments were, in grams per kilogram, (i) none (Check); (ii) 3.98 dolomitic limestone (Lime); (iii) 15.88 high-gypsum flue gas desulfurization by-product (FGD); (iv) 3.98 + 15.88 combination of Lime + FGD; (v) 15.88 high-gypsum FGD by-product containing [approximately]6% Mg[(OH).sub.2] (FGD + Mg); and (vi) 6.45 fluidized bed combustion by-product (FBC). The soil columns were leached with 138 cm of deionized water. Wheat (Triticum aestivum L., 'Arthur') was grown in the columns for 34 d with no additional water. Plants grown in Check and FGD treatments had lowest and similar shoot and root dry matter (DM) and leaf area. Leaf areas and DM for FBC, FGD + Mg, Lime, and Lime + FGD plants were similar and 13 to 17 times higher than for Check plants. Total root length (RL) was highest for FBC plants, which was about six-fold higher than FGD plants, while total RL of plants grown with other amendments was about half that of FBC plants. Specific RL was highest for FGD plants. Plants grown on Lime, Lime + FGD, FGD + Mg, and FBC treatments had higher leaf photosynthetic rates, chlorophyll, and ET and lower leaf temperatures than Check and FGD plants. Even though DM of FGD plants was low, they had the highest leaf relative water content (RWC) and leaf water potential (LWP). Amendments increased soil pH and reduced acid soil stress. Higher mineral nutrient concentrations were noted in shoots of plants grown on amended soil, except for the FGD plants, which had lower Mg and higher B than considered optimal. Some but not all CCBPs benefitted plants grown on acid soil.