Below is a circuit that demonstrates one use of an OTA using an LM13600. Take a note that the strange symbol stand for OTA. In this circuit, negative feedback is employed which is low-pass filter whose corner frequency can be electrically adjusted. We can a filter that would tune from 2700 Hz to 9000 Hz approximately for the values shown.

Voltage Controlled Low Pass Filter with LM13600 OTA circuit schematic

The gain is rolls off at 20 dB/decade and unity below the corner frequency, a first-order response like an RC circuit. The electrical controllability of the corner frequency is the feature which is here simulated by rotating a potentiometer. You will not exceed the maximum 2 mA for the bias current is guaranteed by the 12k fixed resistor. In this circuit, the voltage at pin 1 is -10.8V (two diode drops above the negative supply). The pin numbers for one of the amplifiers are shown, going down the left-hand side of the chip. For other amplifiers, the pins are in the same order on the other side. We have to take a note the unusual location of the supply pins.