Jacobson H R
Am J Physiol. 1981 Jan;240(1):F54-62. doi: 10.1152/ajprenal.1981.240.1.F54.
Early superficial (SF) and juxtamedullary (JM) proximal convolutions of the rabbit kidney were perfused in vitro to determine the effects of carbonic anhydrase inhibition (10(-4) M acetazolamide) and acute changes in PCO2 (decreases to approximately equal to 15 and increases to approximately equal to 74 mmHg) on potential differences (PD in mV), volume reabsorption (Jv in nl x mm-1 x min-1), and bicarbonate reabsorption (JCO2 in pmol x mm-1 x min-1). At PCO2 37 mmHg early JM exhibited a more lumen-negative PD (-7.5 vs. -5.3), greater Jv (1.13 vs. 0.82), and greater JCO2 (86.7 vs. 44.4) than early Sf. Sf and JM had similar responses to acetazolamide: PD became more negative (-5.2 to -5.9 in SF; -8.8 to -10.1 in JM), Jv decreased (0.92 to 0.68 in SF; 1.11 to 0.76 in JM), and JCO2 decreased (35.7 to 7.7 in SF; 99.2 to 27.4 in JM). Increasing PCO2 to approximately equal to 74 mmHg decreased lumen-negative PD, increased Jv, and increased JCO2 in SF and JM (-5.5 to -4.8, 0.72 to 0.95, and 47.6 to 80.4 in SF; -6.6 to -5.7, 1.19 to 1.47, and 78.0 to 111.3 in JM). Decreasing PCO2 to approximately equal to 15 mmHg increased lumen-negative PD, decreased JCO2, but had no effect on Jv in both segments (-4.9 to -5.8, 51.3 to 6.3, and 0.80 to 0.79 in SF; -7.0 to -7.9, 75.3 to 19.6, and 1.34 to 1.41 in JM). It is concluded that 1) early SF and JM display quantitative heterogeneity, 2) PCO2 changes within the physiologic range produce large changes in HCO3 absorption in early proximal tubules and 3) large changes in HCO3- reabsorption are dissociated from changes in volume reabsorption during hypocapnia.
对兔肾早期浅表（SF）和近髓（JM）近端曲管进行体外灌注，以确定碳酸酐酶抑制（10⁻⁴M乙酰唑胺）和PCO₂急性变化（降至约15mmHg和升至约74mmHg）对电位差（以mV为单位的PD）、容积重吸收（以nl×mm⁻¹×min⁻¹为单位的Jv）和碳酸氢盐重吸收（以pmol×mm⁻¹×min⁻¹为单位的JCO₂）的影响。在PCO₂为37mmHg时，早期JM表现出更负的管腔电位（-7.5对-5.3）、更大的Jv（1.13对0.82）和更大的JCO₂（86.7对44.4），比早期SF更明显。SF和JM对乙酰唑胺有相似的反应：PD变得更负（SF中从-5.2至-5.9；JM中从-8.8至-10.1），Jv降低（SF中从0.92至0.68；JM中从1.11至0.76），JCO₂降低（SF中从35.7至7.7；JM中从99.2至27.4）。将PCO₂升至约74mmHg会降低管腔负电位PD，增加Jv，并增加SF和JM中的JCO₂（SF中从-5.5至-4.8、0.72至0.95和47.6至80.4；JM中从-6.6至-5.7、1.19至1.47和78.0至111.3）。将PCO₂降至约15mmHg会增加管腔负电位PD，降低JCO₂，但对两个节段的Jv均无影响（SF中从-4.9至-5.8、51.3至6.3和0.80至0.79；JM中从-7.0至-7.9、75.3至19.6和1.34至1.41）。得出的结论是：1）早期SF和JM表现出数量上的异质性；2）生理范围内的PCO₂变化会使早期近端小管中的HCO₃重吸收产生大幅变化；3）在低碳酸血症期间，HCO₃⁻重吸收的大幅变化与容积重吸收的变化无关。
